For most people, the Power Supply Unit (PSU) of a personal computer is just an afterthought, usually just getting a generic PSU when building a PC. Unfortunately, they’re missing a couple of important considerations when picking PSUs:
Generic PSUs always cheat on their “rated” power.
In other words, don’t expect a generic “500W” PSU to supply 500W of steady power to your computer. Corsair (who sells high quality PSUs made by Sea Sonic) even made a video of them pushing generic power supplies to just 75% of their limit:
Think it’s just a marketing trick from a PSU seller? Unfortunately, it’s not. Some power supplies, especially generic ones, do crash well below their rated power. For example, this power supply crashed at 75% load, with the second sample not even passing the 50% load test (another victim of HardOCP’s rigorous testing).
Cheap power supply makers usually cheat by put a lot of amperes (simply put, watt = ampere x volts) on the 3.3V and 5V rails of the power supply and allocating relatively less on the 12V rails. Now, modern PCs use the 12V rail for most of their components. Therefore, this technique allows the makers to rate the PSU’s power output higher than what the PSU can actually provide the PC.
You could easily verify this by comparing the label of a generic power supply with the label of a “brand name” power supply, say from Enermax, with similar rated power. The brand name PSU will have a much higher amperage at the 12V rails than the generic power supply.
In short, don’t even think of buying a generic power supply if you’re planning to build a gaming rig.
Cheap power supplies are less efficient.
Generic PSUs are cheap because they don’t have the same features as their brand name counterparts. They won’t have power factor correction and they will not reach the same amount of efficiency as the latter.
The thing about efficiency is that even just a 10% difference in efficiency of power supplies can affect your electricity bill, especially if that computer is on 24/7.
Cheaper power supplies are also more likely to fail than their counterparts because the former is made of lesser quality (cheaper) components. Reliability is an important factor for PSUs: anybody who has tried to troubleshoot a PC with weird problems (won’t boot up, suddenly shuts down) will know that it’s hard to isolate the problem to the PSU. (Not to mention that PSUs blowing up can damage the more expensive parts of the PC.)
Let me end this post by saying that there is nothing wrong with getting a generic power supply if your PC is the stereotypical “pang-Word at pang konting Internet lang” family PC. But if you’re planning to add some power hungry components like video cards, or if you’re planning to have your computer run 24/7 downloading torrents, you might want to invest in slightly more expensive PSUs.
As a side note, if you’re planning to build a PC (or if you don’t have an APC UPS), you can use eXtreme Power Supply Calculator to estimate power usage. Just remember that the wattage there would only be applicable to non-“cheating” power supply makers who rate their PSUs properly.