Apart from quality and efficiency certifications, the next major consideration when choosing a power supply is the maximum power output. Power requirements for modern PCs can vary greatly. Entry-level machines with integrated graphics can consume as little as 200W, whereas high-end gaming PCs with multiple graphics cards and multiple HDD setups can require as much as 1000W or more to run them.
A basic way of determining your PC power supply requirements is to add the power requirements of the components it contains. CPU and graphics card manufacturers publish power draw figures for their products. CPUs generally range between 45-95W. Graphics cards vary widely in power draw, with entry-level cards suitable for home theatre use consuming as little as 25W, whereas high-end gaming cards can draw a whopping 300W or even more for some of the recently released dual chip cards such as the Geforce GTX 590 and the Radeon 6990.
Mechanical HDDs draw approx 20W each, Solid-state drives as little as 3W. Don’t forget to factor in the efficiency rating of the PSU you are intending to use. An 80 PLUS certified 500W PSU will only deliver 80% of its rated output; in this case, 400W. It's always a good thing to add a little more than you think you need, just for good measure. If your anticipated power draw figure is 380W, for example, I would be inclined to go up a level or two to a 550W or 600W 80 PLUS certified or higher PSU. This also covers you should you wish to add another HDD down the track, or upgrade your graphics card a level or two. Just remember, a power supply will only output as much power as the components in your PC are drawing, so having a higher rated PSU does not mean that you will be using more electricity.
The final decision to consider is whether to pay a little extra and purchase a modular power supply. Most high-end PSUs are modular as standard.
A modular power supply has a collection of cables that plug in to the body of the PSU, and only need to be added as required. A traditional power supply has a large collection of cables, with a range of different end plugs, all hard wired into the body of the PSU. This can often create a large spaghetti-like mess of unused cables cluttering the inside of your PC. A good technician will usually try to tidy all the excess cabling, as it can impede air flow through the PC case and restrict cooling, or even worse, loose cabling can lodge in cooling fans, jamming them completely, and leading to overheating issues. A modular power supply helps solve these problems by letting you plug in and use the minimum number of cables necessary to power the components inside a PC.
Hopefully the information presented here will empower you make an informed decision, when next it comes time to consider the purchase of this most critical system component. A good quality power supply is the first building block of a good quality PC.
Glenn Howlett is the general manager of DCA Computer Technologies a computer retailer and support provider. Read more articles at the DCA Computers blog, follow DCA Computers on Twitter and become a fan on Facebook.