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.

Tags pc componentspower supplies

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Glenn Howlett

PC World

9 Comments

Gordon Drennan

1

There are a number of errors in this article.

The writers says mains power is 240V in Australia. It is in fact 230V.

The writer says that a PSU with an 80% efficiency can only deliver 80% of its rated output. This is wrong. A PSU rated at 400W, but if it only has an 80% efficiency to do that it will have to draw 500W from the power point.

PC World should find someone who knows the subject better to write advice for its readers. Perhaps someone who isn't the manager of a retailer that benefits if customers buy higher spec'd and higher priced products than they actually need.

Pete

2

Gordon, Australia may well be a 230V country now, but mine and my friends places still put out 240V. What do you get at home? Either way, one of the things i looked for when buying a PSU is a 240V rating (not a 230V one).

Grant

3

You are mistaken Gordon. The domestic mains power supply in Australia is 240V AC, 50Hz. Any sparky knows this:
http://www.accesscomms.com.au/reference/powerplug.htm

As for your other comments. Well you are wrong again.

What do you think the 'Plus 80' system is all about? The writer is spot on. You need to check your facts before you burst into print.

Patrick

4

@Gordon... Everyone knows that Australian outlets are 240v, any electrician will tell you that to.

Ben

5

Gordon.

Don't you know that Australian outlets are 240v??

Gordan???

Hello?

Gordy...........

Back in your hole mate

Ben

6

I think the only error in this article may well just be the first comment

mattgenton

7

hi to all at www.pcworld.idg.com.au i thought i had sent this newyears eve but it didnt send so i have sent it again all the best for new year to every one
- matt-gent

mr tired

8

Gordon gordon grodon If you are in fact a MALE then you are an idiot. THIS IS SPARTA Know what thats from

Hello

Hells kitchen

Wheres my cat

wheres my dog

wheres my FACE

MT

9

Gordon is 100% correct on the efficiency aspect of the article. A simple look at Wikipedia will already give the correct definition of PSU efficiency. Try to claim a 500W 80% efficiency PSU can only supply 400W on any PC enthusiast website and you will have people laughing their heads off.

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