How to choose a power supply for your PC

A guide to buying the best PSU for your computer

Ask any good computer technician what the most important component is in your PC and the likely answer will be the power supply (also known as the PSU, or power supply unit).

The PSU is designed to take an input voltage from mains power (here in Australia we use 240V) and then reduce and regulate the output to 12V or less, to power the components inside the PC. Looking at the power supply you will see a range of different plug connectors, designed to power such things as motherboards, hard drives, optical drives, and graphics cards.

Most manufacturers will give a power rating to their particular PSU models such as 500 Watt or 850 Watt. Most people tend to think that the power rating of the PSU is all they need to know, but this is not the case. There are very good quality high efficiency power supplies on the market, but, conversely, there are many poor quality PSUs on the market also. Some cheap and nasty PSUs are lucky to achieve a sustained output of half their claimed power rating, meaning that your new 500W PSU may indeed only be capable of 250W of continuous output. Certainly not enough to power your new high-end gaming system!

In an effort to rationalise the labelling of PSUs and to promote energy efficiency, industry leaders devised the 80 PLUS rating system as far back as 2004. The 80 PLUS idea created a list of efficiency specifications that a PSU model needed to achieve across a range of their rated power loads. Any PSU submitted for testing which was able to meet these requirements was then awarded an 80 PLUS rating and is allowed to advertise this certification, as well as use the 80 PLUS certified logo. In early 2008 the 80 PLUS standard was revised to cater for newer, more energy efficient models and the 80 PLUS Bronze, Silver and Gold categories were created. To this list was added the 80 PLUS Platinum certification in October 2009.

Below is a table for Internal Non-redundant Power Supplies and the efficiency rating required at 20% load 50% load and 100% load to achieve certification in one of the 80 PLUS categories.

Fraction of rated load20%50%100%
80 PLUS 80%80%80%
80 PLUS Bronze 82%85%82%
80 PLUS Silver 85%88%85%
80 PLUS Gold 87%90%87%
80 PLUS Platinum 90%92%89%

As you can see by this list, the most energy efficient Gold and Platinum rated PSUs are averaging close to or slightly above 90% of their rated output.

Some unscrupulous companies have used the 80 PLUS logos in their advertising or on the product packaging, when in fact their PSU has not been tested or certified. At DCA Computers we see such impostors on a regular basis. The eager vendor will put his hand on his heart and swear the unit has 80 PLUS certification while holding up a PSU that is adorned with a bright gold 80 PLUS sticker. Apart from the PSU being not much heavier than the cardboard carton it emerged from, it’s hard to tell the difference. When the PSU is fitted into a tower case, it then becomes a more challenging ruse. The only way to be absolutely sure that you are getting the genuine article is to check the validity of any certification claims by going to the following website. This site lists all manufacturers and models which have had certification status awarded to them. So far 2824 PSUs have been awarded 80 PLUS or higher certification, so there are definitely plenty of quality choices currently available on the market.

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Glenn Howlett

PC World
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