Why Your Power Supply Choice Is So Important
Your computer’s power supply, or PSU, is a critical part of your computer. It has to supply the exact or near exact voltage at the required wattage to all of the circuitry inside your computer. The processor and memory are particularly sensitive and require an exact supply or as near as possible to one.
So, why does your choice of power supply matter so much when building your rig?
Despite the sensitive voltage and current regulator circuitry on most motherboards; generally adjacent to the processor (CPU) or memory (RAM) itself, the supply of power to the motherboard with respect to these components needs to be as near spot-on as possible. If your power supply unit (PSU) has trouble delivering that then strange things start to happen.
Your computer may start acting strangely or even produce repeated stop errors or blue screens of death. (BSOD) The event logs may record these as being due to memory errors, and probably correctly so, but the memory errors could be being caused by an insubstantial power supply to the RAM and/or CPU.
Why would this occur? There are a number of reasons that this may happen. The most obvious being that the PSU is wearing out and needs replacing.
Power supplies, like most other computer components, don’t last forever. How long they actually do last can depend upon the quality of the unit as well as the demands being made of it. A cheap and nasty supply may not be capable of delivering its stated wattage. If you’re loading it heavily by running a lot of hardware, it may actually produce a significant voltage drop across its output due to the high load. In fact, Computer Shopper magazine tested a number of different makes and models of power supplies for reliability during 2007 ( – And tested PSUs again during 2008.). One of the tests was to run the PSU under test at full load to see if it could deliver the wattage stated on the tin. Not many of the thirty or so PSUs under test could actually do so, although over half came near to the mark, supplying only a few tens of watts less than claimed. The cheapest PSUs were undoubtedly the worst in this test; with the cheapest PSU actually failing totally with a 500 Watt load, and another of the cheapest models literally blowing up in a self-detonation!
Straining a power supply results in heat building up within its components, as does the act of simply running it. I’ll rephrase that: Heat builds up within a power supply when it is being used, and straining a supply causes excessive heat to build up in its components. Heat is an electronic component’s enemy. It causes chemical changes within the component’s chemical structure which causes the individual components to become less effective. Overloading a supply will wear it out much quicker. Bearing in mind that many PSUs are unable to actually supply their stated Wattage, your PSU may be overloaded without you actually realizing it, especially if you’ve added new hardware such as an SLI graphics-card or similar.
Even if the above is not the case, power supplies don’t last forever. If you’re experiencing random frequent crashes it could be that the power supply requires replacement. (It could also be due to a phenomenon known as “capacitor plague“.)
Power supplies aren’t immune to power surges from the electricity grid, either. A large voltage spike, or even a brownout, where the mains voltage drops and fluctuates wildly, can in rare cases damage them – as well as, more likely, your other hardware. That’s why it’s always a sensible idea to run your mains power through at least a surge-protector, or better still a UPS, before connecting it to your system.
Finally, if you’re building your own computer or replacing the PSU in your existing box, then my advice to you is to calculate the combined wattage used by all your hardware, and buy a power-supply unit that’s rated around 100 watts greater than that figure. That way, providing you don’t buy the cheapest PSU available, you should have a certain amount of wattage to spare if your computer’s components require extra power at any point.