How To Choose A PC Power Supply

by Rustam Iqbal

Picking a suitable power supply for your PC is critical as it can ensure that the hardware you have installed works with stability and reliability. A bad or underrated PSU can lead to equipment failure or undetectable random crashes. You must learn how to choose a PC power supply ( AMAZON ) to ensure the healthiness of your equipment.

What Is PSU?

What Is PSU?

Your computer components run on Direct Current (DC) instead of Alternating Current (AC). When you connect your computer to the wall, you provide an AC source and the PSU changes it into DC to be electronics-friendly.

A power supply has a variety of specifications to detect performance like power, modular capability, energy efficiency, protections, outputs, connectors, mean time to failure (MTTF), cooling system, dimensions, and certifications.

We intend to ensure that you find the correct power supply for your computer by carefully examining its specifications and evaluating the system requirements. There needs to be a clear understanding of what these terms mean and the variety of options you will have to deal with to achieve analytical skills.

As easy as it seems, picking a random PSU from the market for your PC is not a wise choice. An analysis is required to find the best fit for your build.

Power Output: How Much Do You Need?

Power Output: How Much Do You Need?

A power supply is meant to fill the energy requirements of your PC components. The power rating reflects the ability of the PSU to convert the alternating current to a direct current considering the power.

If you demand higher power than the power supply capacity, it will cause it to heat up, eventually damaging the components of the PSU or your computer hardware. The Central Processing Unit (CPU), Graphics card, RAM, Motherboard, RGB lighting,Cooling system, RAM, and connected devices will all contribute to the rising power demand.

Knowing the power consumption of each device is essential to calculate how much power you need for stable operation. Manufacturers always mention the power consumption of their devices in the specifications of the product. However, if you are having difficulty finding it, you can use PSU calculators from multiple websites to determine your requirements.

The leading equipment which consumes the most power is the graphics card and CPU. A typical high-end graphics card consumes around 450W of power, which is very high compared to high-end RAM which consumes a maximum of 6W.

So excluding the power consumption of other hardware, only the core hardware will require a 700+W of power supply capacity to function correctly. To ensure some overhead space, you must find the proper power consumption with all the peripheral devices and then multiply the calculated value by x1.1.

Why do you need an overhead space? We will explain it in the next section of our guide.

Pick That The PSU That Supports Upgrading

Pick That The PSU That Supports Upgrading

Anticipate Upgrades When Buying A Power Supply

One of the most remarkable features of a modern-day PC is the ability to upgrade. You can enhance the computer’s capabilities by installing new devices or simply replacing old ones. Upgrading or installing new devices may lead to higher power consumption.

The power drawn after upgradation may cause the PSU to become underrated, which is dangerous for hardware. As users, we need to anticipate future upgrades and add that wattage into our initial PSU power calculation. For example, you might use an entry-level AMD Ryzen 5 7600X CPU in your initial build.

It consumes 180W of electricity at peak loads. Later, you might consider upgrading to a high-end AMD Ryzen 9 7950X that consumes 230W of electricity at peak loads. The difference is around 50W for the upgradation of the processor alone. There is a difference in heat production as well, which may lead to the upgradation of the cooling system if you haven’t incorporated anticipated thermal load increases in the future.

It will also affect the PSU power requirements. We hope you got the theme. If you are worried that a higher power PSU will lead to higher power consumption, there is nothing to worry about. The higher power PSU will contribute to the initial cost of your PC build. Still, it will not increase power consumption as it depends on the component’s power requirement rather than the PSU’s ability to supply power.

After you have calculated the necessary power, we recommend multiplying the figure with x1.1 to ensure that you have a margin for peak power.


Computer hardware is a significant investment; protecting it is vital to eliminate loss. As we mentioned earlier, if a power supply is underrated, this will cause it to heat up and eventually fail. A sub-standard power supply may damage the downstream equipment.

Manufacturers have incorporated protections in the PSU to protect equipment, which adds to the unit’s overall cost. There are three primary protections: overvoltage, overload, and overcurrent protection. Overvoltage protection means that the power supply will cut off the supply to the PC components in case high voltage is detected in its input.

High input voltages to the power supply will lead to increased output voltages to the PC hardware and cause damage. The overload protection detects if the power consumption has increased beyond the device’s design. It usually causes the supply to shut down when 110% to 140% of the design value is reached.

It is slower compared to the current protection. Overcurrent protection is faster and continuously monitors the amount of current being drawn by the device. It immediately detects any short circuit and shuts down the computer.

Overtemperature protection is mainly designed to protect the supply unit. If a fan failure occurs in the supply unit, it will cause the equipment to fail or the insulations of the transformer to be damaged. A thermistor detects the temperature and immediately cuts off the current supply to protect the unit.

Efficiency Matters With A PSU

Efficiency indicates how much the PSU will require input power to produce the desired output power. For example, an 85% efficiency power supply providing a demand of 700W will pull 823W from the wall power socket. Comparatively, a 70% efficiency supply for a similar 700W output will require 1000W power from the wall. It’s a simple formula:

Power Drawn from the Wall Socket = Efficiency x Power Rating of the PSU

Where does the extra power go? It turns into heat produced by the components. Lower efficiency equipment will lead to high energy bills and heat production inside the computer chassis. The heat production will then require removal, which will be done by using fans, adding more power consumption.

A high-efficiency supply will reduce the energy bill and produce less heat but have a high initial cost. The sweet spot depends on the build and users’ preferences.

What Is 80 PLUS Certification?

As we mentioned earlier, a user preference would lead to a sweet spot where the cost and benefit are balanced against efficiency. While taking efficiency into account, we will help you choose a PC power supply. Usually, when buying a power unit for the computer, you will see 80 PLUS certifications for the equipment.

It represents the fact that the supply has above 80% efficiency. In most cases, after a cost-benefit analysis, equipment with 80% or higher efficiency is considered good quality. They have given different names to different supply classes, as shown in the table below. It starts from 80% and goes to the Titanium edition with 90%+ efficiency.

When you look at the modern modular power supply unit, you will find multiple ports on one end, labeling +3.3V, +5V, +12V, and more. You will find the power limit for each port beneath them; these are called rails. You will find multiple +12V rails when you buy a PSU. A non-modular unit will not have ports; it will come preinstalled with wires, and you cannot install custom-colored cables.

Modern power supply units are primarily modular, which allows the replacement of cables and color matching with the chassis. We will focus on the modular type as it is the best option in the market.

The most power is drawn through the +12V rails as they supply the Central Processing Unit (CPU) and Graphics card, which are power-hungry. The motherboard usually has two 8-pin connector requirements for providing CPU and RAM. Then depending on the graphics card, there could be two 8-pin connectors on the graphics card. Why do you need multiple +12V connections?

It’s because each +12V rail has a power limit represented in amperes. Manufacturers mention the limit power for individual rails, and it is done to protect the other equipment connected to different rails. If a single powerful rail uses a short circuit in one hardware, it will lead to the failure of other components as they are all connected to a single rail. Multiple rails provide the benefit of equipment protection.

You must go through the power supply specification to ensure that you have enough power flowing through each rail to support the load downstream. A high-end graphics card that needs a 550W of power supply requires two 8-pin connectors.

If we connect a wire to a single +12V rail port and use a splitter to have two 8-pin connectors connected to the graphics card, then the required ampere rating of a single rail would be 46A. However, we can use multiple rail ports to supply one graphics card, decreasing the ampere requirement of a single rail connector.

However, you cannot simply combine two rail ampere ratings, for example, +12V1@38A and +12V2@38A; supplying a simple graphics card might have 70A output compared to the 76A. Read the manufacturer’s manual to understand how combining two rails for one piece of equipment will result. Be sure that the power requirement of equipment is met.

Pick The Size You Need!

Pick The Size You Need!

Form factor – Will your power supply fit?

The form factor is similar to the sizes of your PC case. You want a power supply that can fit into your favorite case. Manufacturers have standardized their product dimensions concerning the PC case standards. It is now easy to find the best fit. It would help if you were careful about compatibility with the motherboard.

There might be some limitations due to the smaller supply size, so we need to consider them before selecting our PC case, motherboard, and PSU. There are many choices, but we will mention the most common example:


If we talk about legacy products, ATX has been around for decades. The technology is mature but has been outdated after the introduction of the ATX form factor. There are a few differences between the two, so we believe that mentioning them is crucial:

  • +3.3V rail was not present in the previous generation ATX 2.03 and earlier.
  • The 20-pin connector is a standard power supply cable to the motherboard
  • The software can now turn off the power supply through feedback from the motherboard.
  • An ATX power supply is a standard 150mm width and 86mm height. However, the depth can vary depending on the manufacturer.


ATX12V is a common choice of most PC builders. However, it comes in different versions, each with its features. To make things easy, buy the latest generation of ATX12V power supply to avoid hassle while selecting. To better understand ATX12V v1.0, the first iteration of the ATX12V design added a 4-pin +12V connector, which supplied power to the CPU, and a 6-pin aux connector. The later ATX12V v1.3 added a 15-pin SATA connector.

Traditionally, the motherboard was supplied by a 20-pin connector similar to the ATX. As an iterative improvement in the ATX12 v2.0 added a 4-pin connector to provide a 24-pin connector. In contrast, they removed the additional 6-pin dedicated power connector for the CPU.

The improved power limit to the supplied power cord and different rails came later. The dimensions remained similar to the previous ATX versions, which are 150mm by 86mm with varying depths.

EPS12V, SFX12V, And Others

In terms of dimensions, the EPS12V looks similar to the ATX power supply. However, the main difference is that the EPS12V stuck to the 8-pin power connector, whereas the ATX12V evolved with time. It is designed mainly for server PCs and desktop PCs with high-end configurations.

If your motherboard requires a dedicated 8-pin connector for the CPU, then the EPS12V is the way to go. When buying a chassis, we look for terms like full-tower, mid-tower, mini itx, and SFF (Small Form Factor); power supplies come in similar dimensional labels.

SFX12V (Small Form Factor), CFX12V (Compact Form Factor), LFX12V (Low Profile Form Factor), and TFX (Thin Form Factor) are some of the names given to power supplies that are smaller in design.

They are designed to fit tight enclosures ideal for HTPC and gaming consoles like PC builds.

PSU Connectors

PSU Connectors

Let’s move on to the hardware connection end of the power supply. There are 8-pin connectors, 24-pin connectors, and a 4-pin Molex connection to supply power to the hardware. All of them are designed so users cannot plug them the other way around.

The standard connector for optical drives, storage devices, RGB lighting, fan systems, etc., is a 4-pin Molex connector. With time and iterative design improvement, 24-pin motherboard connectors are now standard practice. There is a dedicated 8-pin connector to supply power to the VRM on the motherboard. The VRM then converts the voltage to the desired value for the CPU and RAM.

Pick The PSU With Silent Fan!

Pick The PSU With Silent Fan!

Fan Noise And Cable Convenience

We have discussed the dimensions, types of connections, ratings, and rails, but there are a few things we need to consider alongside these factors.

Fan Noise

Low-noise PC builds are now becoming the focus of gamers and creators. The fan-built quality can influence noise, longevity, the flow of air, and power consumption.

As we discussed earlier, a power supply has a particular efficiency at which it operates; the rest turns into heat. If we subtract the output power from the input power, we will get the approximate heat production. For example, if we have a 1000W power supply with 90% efficiency, there will be 100W heat production. To remove that heat, you need a fan.

High-flow fans are not ideal in computers as they produce a lot of noise and do not have enough power to push the air through the densely packed hardware. Static fans with high static pressure are ideal; they produce less noise. Their built quality is also essential; Bearing design directly affects the MTTF (Mean time to failure).

As the bearing wears, it will create noise and reduce airflow. Make sure that your power supply has a high-quality fan.


We wanted to include cabling in our guide on how to choose a PC power supply as it can improve aesthetics and provide ease in installation. There are mainly two types of power supplies: Modular and Non-Modular. Traditionally non-modular type power supplies unable to change power cables were standard.

It possessed certain limitations, which included the use of splitters for providing two hardware devices from a single rail. A fixed color sheath was available, and users couldn’t change it at any point.

Modular comes with replaceable cables, which users can change with the desired connection from a single rail.

Aesthetics improved drastically by allowing users to select the colors they like per their computer build. Users could use suitable cable ties for cable management with ease.


We tried to help explain how can you pick the best power supply for your PC and how is it important to go for the right product. Because the good power supply will be able to provide clean, stable power to your PC components, which will help to prevent crashes and other problems.

It will be able to convert AC power to DC power with minimal loss, which will save you money on your electricity bill. It provides enough power to your PC components, even when they are under heavy load. This will help your PC to run smoothly and efficiently. A perfect power supply will have safety features that will protect your PC from damage in the event of a power surge or other electrical fault.

Consequently, a good power supply will come with a long warranty, which will give you peace of mind if it fails. If you are looking for the best possible performance and reliability for your PC, then you should invest in a good power supply.

It is one of the most important components in your PC, and it will make a big difference in the overall performance and longevity of your system.

Rustam Iqbal

Hi, I'm Rustam Iqbal. I love traveling, computer hardware, and software. I’m constantly trying to learn new skills and programming languages. Reviewing new pieces of hardware is one of my favorites hobbies. Drop by any time to leave me a message if you have any questions.

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