Selecting a power supply for a custom PC is not rocket science but it’s also not common sense. There are several components and decision factors that play into which power supply you select.
The first and obvious decision to make is how many watts you need. All power supplies are measured in watts and named after their wattage.
If you’re running two monitors, a high end graphics card, high end processor, liquid cooling, 32GB RAM, NVMe M.2 drives, and you’re gaming 2-4 hours per day, then chances are you won’t need anything more than 550W PSU.
Keep in mind that buying a higher wattage PSU won’t hurt and since the price range is trivial, you might as well go for a 750W PSU. Regardless of the PSU wattage, your PC will only consume what it needs and no more. Your power supply will also only draw as much as it needs from the wall outlet.
To be certain of how much watts you will need your PSU, you can use a power supply calculator, like the one provided by OuterVision:
It is always recommended to err on the side of buying a higher wattage PSU. Buying a PSU that is underrated for your system can cause a lot of problems. Problems getting your PC to power on, seeing blue screens and system crashes are symptoms of the PSU not delivering enough power.
Power Efficiency
Another factor in selecting a power supply is its efficiency rating. You will see the efficiency rating denoted as 80+ something. Something is either titanium, platinum, gold, silver, or bronze. The better power efficiency is, the more efficient the power supply is at getting and delivering power to motherboard components. Less efficient power supplies conduct more heat and draw more power than needed.
Modular vs Non-Modular
Modular power supplies are a little more work than non modular power supplies. With modular power supplies, you can opt to only plug in cables that are actually needed for the functionality of your PC. While this improves cable management, you do have to manually connect cables both into the motherboard and into the modular power supply. The non-modular power supply comes with cables soldered into the power supply. Even if you don’t need the extra cables, you have them. It’s not great for aesthetics, but it does reduce some workload as you’re only responsible for plugging in one side of the connections.
Form Factor
Always double check the form factor of the power supply you are buying. The last thing you want to do is to be 90% finished with your custom PC build, then try to slide your power supply in only to find out it doesn’t fit in the case. Make sure that the form factor of the power supply matches the dimensions of the opening on the case.
Selecting a power supply is easy once you understand how much watts you need and the form factor. The extra power efficiency is nice to have if you can afford the few extra dollars and modular vs non-modular power supplies is a preference decision.