Ask any good Computer technician what the most important component is in your PC and the likely answer will be “The Power Supply Unit” or PSU for short.

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 & 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 labeling 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.

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 imposters on a regular basis. The eager vendor will put his hand on his heart and swear the unit has 80 PLUS certification whilst 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 fastened into a tower, 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. At the time of writing of this article 2824 PSUs have been awarded 80 PLUS or higher certification, so there are definitely plenty of quality choices currently available on the market.

http://www.plugloadsolutions.com/80PlusPowerSupplies.aspx

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 using 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. Its 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 which 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 only having to plug in and use the minimum number of cables necessary to power the components inside your 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.