Power Supply Unit (PSU) Selection

Written by: Joe Egan

Planning to build a new system and…… what’s on your list? Perhaps a Motherboard, CPU, GPU, RAM, Hard Drive, DVD or Blue Ray Reader\Writer? Of course, don’t forget the power supply which will only cost around £25 but surely you will spend around £750 from the hardware list that you are about to build and you’re scrimping on the most important part – after all, the recommended power supply for the graphics card is 500watts, right? That’s wrong, because that is only for the card and not what you are going to invest on each component that will draw power from the PSU so not factoring that it is in the recipe for disaster as is choosing a cheap made PSU. Think about it, if you have to spend £750 on the rest of the components and you’re not prepared to spend a reasonable amount on something that makes it all work – the PSU.

Let’s face it, £25 is not even 5% of what you will need to spend to build an entire system, but it will run the system okay and it may do the work but as I’ve previously mentioned buying cheap components means trouble. Also, a cheaper PSU will not help ensure a degree of safety for your other hardware but it will overload and cut out heat. There are many more features that could be mentioned but in order to keep this from being overly technical, more of these can be found by simply doing web searching.

There is a myriad of information out there covering things like the 12v, 5v and 3v rails, power factor correction etc. Let us keep things simple and be sensible, look at certain things and I know there are folks who would say I could never afford to spend a lot for a new system and that is fair enough. The amount you spend will be proportionate to what you personally can afford. The point is…. you should make the power supply a big priority and not a last minute stop shop. A cheap PSU will probably fail at some point in a short period of time and without the safety features it will likely kill your other hardware components and that is a greater hit to your pocket than buying a good quality PSU.

A power supply using the latest ATX standard v2.3 is advisable making it more energy efficient on all motherboards made in the last five years that support this standard. Wattage is also vital; you should calculate the amperes required for all hardware including motherboard as minimum requirement. The power supply should be on the 12V rail and match or exceed the minimum requirement for amperes of all your hardware before adding 30% wiggle room for future upgrades and degradation of power supply over time.

Using a power supply certified for 80+ either Bronze, Silver or Gold certification will be more energy efficient and complies to Energy star 4.0 standard and incorporates the safety features mentioned previously.

A couple of PSU brands that comply to 80plus standard and are great units are:  Seasonic, XFX and Corsair (Seasonic Subsidary).

To help you with what the right one to select there are online resources, a good example is technical forums where people like myself will be happy to help you through the maze of selecting not only your PSU, but all the hardware you would require to make the best build within your budget.

A simple rule of thumb is to remember that power supply is made within a tolerance of typically + or – 20% with the cheaper supplies it will be more in the minus area. When selecting the right power supply find the minimum requirement and add around 30% or more if you wish. I would say 30% is a pre-requisite when choosing a power supply to allow for hardware upgrades and degradation of power supply after first year and onwards.

And….. last but not the least; a bigger power supply will not add to your electric bill as the system only uses what it needs. Ahh….. I hear you say why get it if  some point that you may decide to upgrade some hardware or add more, don’t forget the peripherals many will need to draw power from it.

Here are some online resources links to help you with your PSU selection:



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