How to choose a PC power supply- Senxios


Building a PC isn't a straightforward job, a certain level of experience and technical knowledge is needed when choosing the right components for your PC. The PSU or power supply is no different, being the basic source of life for your PC, buying the right PSU is crucial. Let me help you make that decision.

pc build

Table of contents

First things first

Specifications that matter
      What’s Next?

      First things first

      How much wattage do you need?

      The first step to take before buying a PSU is to evaluate how much electrical power your PC will require.

      The easiest way of doing this is by using online tools which have become increasingly sophisticated, to effortlessly calculate the overall power (in watts) needed by your PC to operate.

      Once you have the wattage that you need, you should add some extra room to it for future-proofing. For example, if your PC currently requires 600W of power you should buy a PSU with a capacity of 750W or more, so you can don’t need to upgrade your PC's power supply later down the line when you consider upgrading it. 

      Also, do not worry about buying a power supply with more capacity than needed. It will not increase your electricity bill, as the PSU will only consume the electricity needed by your PC even if it has a larger capacity.

      Understanding connectors

      Keeping the required connectors in mind when buying a PSU will save you a lot of time and effort. If you own a modern PC, it won't be a problem but if you own a budget PC that likely houses older components you will need to buy a power supply with the right connectors.

       power supply connectors                             

      The 24-pin connector is the largest connector you’ll see in your PSU and this is used to power your motherboard and has stayed the same throughout time.

      The 4/8-pin connecter will either have four or eight pins. This is used to power the heart of your PC, the CPU. Previously the 24-pin connector was enough for the CPU too but newer CPUs require a lot more power so a separate connector is used.

      Therefore, you should know which connector your CPU and motherboard support before buying a PSU.

      The 6/8-pin connector usually powers the GPU. Often other slots are used to power the GPU, sometimes a PCIe slot is used as well as a separate cable depending on how much power your GPU needs. Hence keeping the power needs of your GPU in mind is of utmost importance when choosing the best PSU.

      The 4-pin Molex connector is used for powering older HDDs and water pumps, in the case of water-cooled PCs. It is increasingly becoming a legacy connector as newer PSUs house a separate SATA slot to power HDDs.

      Lastly, the SATA connector is used to power SATA storage devices and even RGB lights and fans have started to utilize this connector.

      Choosing the right form factor

      Many PC casings now have standardized sizes for catering to different consumer needs; this means not all PCs have the same amount of space available in their casings.

      power supply in case


      That is where the PSU form factor comes in, for the consumer's ease, PSUs are offered in different sizes so they can fit in different PCs. Therefore, you should match a PSU with your motherboard and casing.

      The most common form factor was AT which is now being phased out in favor of the newer ATX12V, also simply knows as ATX, form factor which has now become the mainstream form factor for all PCs. ATX has a width of 150mm and a height of 86mm with a depth of 140mm. This can fit in almost any normal-sized casing.

      For smaller cases, smaller form factors of PSUs are offered such as the SFX12V, where SFX stands for the small form factor. Similarly, other smaller PSUs like the CFX, EPS, and TFX are also offered, being smaller than ATX they can cater to the needs of consumers who have small compact PCs with limited space.

      Specifications that matter


      When PSUs are discussed “rails” are often mentioned.

      Rails are the paths that deliver power to all the components of your PC, they are printed on a circuit board.

      The label on your PSU usually has the rails and their voltage mentioned on it.


      power supply rails label


      Power is provided to the components by rails, and while each voltage rail requires attention, the most important one is the +12V rail(s) that provide power to the most power-hungry components of a PC: the CPU and the graphics card.

      PSUs can have a single rail or multiple +12V rails. Power supplies with more than one rail are known as multi-rail PSUs.

      A modern power supply must output at least 18A (amps) on the +12V rail(s) for a mainstream up-to-date computer, more than 24A for a system with a high-performance graphics card, and sometimes up to 34A for ultra-high-performance rigs. 

      The output amperage is the sum of the amperage for each individual rail multiplied by the number of rails in the power supply.

      Each power supply has a different number of +12V rails, so it can be difficult to figure out the total amperage.

      For instance, a PSU with rails labelled +12V1@18A and +12V2@16A may only have a 30A combined power output instead of 34A.

      Something you should know about multi-rail power supplies is that while they offer added flexibility, they can sometimes limit the available current.

      For example, if you connect 26A worth of components to a +12V rail with a 20A max rating the mismatch will trigger overcharge protection (OCP) and shut down the whole PSU even if other rails are available. 

      Though this can be an inconvenience, it also protects the PC in case of power surges as the OCP will shut down the PSU just in time.

      Whereas in single-rail PSUs the OCP kicks in at a much higher amperage and this can lead to a major meltdown.

      You can easily find this information in the detailed item specifications or on the PSU information label.

      Both types of PSUs perform similarly, so which one will be better for you? That depends on your PC’s configuration.

      Rails don’t matter much in low wattage PSUs but if you have a high performance GPU or CPU for gaming and will use a high wattage PSU, getting a single-rail one would be much better. The single rail PSU will not shut down even when these components are drawing large amounts of current; the only compromise will be on the safety side of things as OCP kicks in at much higher currents in single-rail PSUs, which can cause damage.

      That too will not be a problem if you use an external circuit breaker or stabilizer.


      Efficiency is vital to the performance of your PSU. Efficiency means how much energy is actually being used to power your PC and not being wasted as heat energy. For example, if your PSU is rated at 600W but has a 50% efficiency, 300W will be lost as heat energy and it will actually pull 900W from the wall socket causing a dramatic increase in your electricity bill.

      A PSU with higher efficiency will not only use less electricity but will also heat up less, reducing the load on your fans giving you a quieter experience.

      To gauge the efficiency of all the PSUs available in the market, an efficiency certification exists known as 80 Plus certification, every PSU with an efficiency of 80% or above.

      This certification has been further categorized as metals depending on their efficiency, these categories and their corresponding efficiencies under different loads are mentioned in the table below:

      80Plus efficiency categories:

      % of load





      80 Plus





      80 Plus Bronze





      80 Plus Silver





      80 Plus Gold





      80 Plus Platinum





      80 Plus Titanium





      The 80 Plus Titanium certified power supply offers the best efficiency and will run cooler and quieter than other PSUs, these PSUs are often high-end PSUs and will be a little out of budget for the average consumer.

      Nevertheless, you should always pay attention to the 80 plus standard of efficiency when buying a PSU and buy the highest quality one that falls within your budget.


      As you would expect from anything that deals with large amounts of power, safety is a concern.

       A good power supply should have built-in features not just to protect the PSU itself, but also to keep your PC safe in case of something unexpected, like a power surge.

      The power supply and the motherboard are the only PC components that directly connect to almost every other piece of hardware in your system. Because of the crucial position of the PSU in the PC’s electric layout, making sure it has built-in protection can help keep the rest of your components safe as well.

      It is worth looking for a power supply that has built-in protection, like OVP (Over Voltage Protection) or OCP, which shuts down the PSU if it is ever overloaded.

      Other safety features include functions like short circuit protection, which can be massively beneficial if you often face power fluctuations.

      You’ll also want to plug in your PC to a surge protector. These hardware-saving devices are designed to add another layer of protection to your system by diverting potentially damaging power surges away from your components.

      Cable management 

      Everyone wants their PC to look clean and uncluttered and if there’s one thing that hinders that wish from becoming a reality are exposed wires and cables.

      Cable management image                   

       Choosing the right PSU is vital to keeping your PC how you want it to be in terms of cabling.

      PSUs depending on their types of cables are classified into three different sections: non-modular, semi-modular and fully modular.


      Most low to medium-end PSUs are non-modular. This means that each cable is directly connected to the power supply whether it is needed or not, wires can’t be removed and you would have to deal with them somehow, usually just shoving them in an empty crevice in your case. 

      This isn’t very good for airflow and it will be much more difficult to replace parts in the future.

      If you don’t want the clutter of wires and want to choose which connections you need, you can spend a little extra and buy a PSU with semi-modular cabling which is a mix of both, some cables are attached and some aren’t.

      These PSUs are usually medium to high end and give you a lot of liberty while choosing which connections you want. These PSUs though are a bit costly but are the key to keeping your PC uncluttered and clean, less cables also make maintenance easy. I highly recommend investing in one.

      Modular PSUs come with no cables attached, it is up to you to make sure that every cable that you need is attached. This will nevertheless add a bit of complexity to your PC and is a bit overkill. Not only that but modular power supplies cost much more than the previously mentioned options.


      There are thousands of power supplies available on the market, since it is vital to almost all other components of your PC, choosing the right PSU for your new PC is essential.

      If you spend a little time weighing your options and carefully considering all the above-mentioned factors when making a decision, it would go a long way for you in terms of having a hassle-free experience with your PC.

      Always prioritize reliability and quality over price when buying a PSU as a bad PSU with no protection or low-quality materials of manufacturing can cause major problems down the line. Always look for quality certifications and well-reputed manufacturers.

      With this information and a little confidence in your decision, you are now ready to go out there and buy a power supply!

      If you have any questions feel free to contact me, you can use the comments section below or a contact form.

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      What’s Next?

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      • Rohit


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