Power supply buyers guide

Power, how much do I need?

This is one of the most important questions when building a PC. Firstly take a good look at the Amperage that the different circuits in a PSU can deliver. The maximum power as stated by the manufacturer is usually not a good indication of what the PSU can actually deliver. As a guideline, a budget PC will require around 20A on the 12V circuit, a normal desktop PC will use around 25V and a high-end gaming machine will require at least 36A on the 12V rails. As stated before, when building a high-end machine choose a PSU with two 12V rails, three if you plan to use Crossfire or SLI.

PSU's generally do not deliver the exact 12V, 3.3V or 5V on a rail: it is usually a bit above or below these values and will drop as the load on the machine and PSU increases. Official PSU specifications state that system stability will be guaranteed as long as the voltage does not differ more then 5% from these values. In practice this means that the 12V has to provide at least 11.4V, the 5V 4.75V and the 3.3V circuit a minimum of 3.14V. In our database you will find the maximum load that we can put on all recently tested PSU's before the voltages drop below the recommended values. We have found that while most PSU's cannot deliver what they promise in their specifications, we have also tested PSU's that can take a lot more than the manufacturer promises. As we cannot do a test on a PSU of hours or even days, our results might be a bit better than the specifications. It is therefore not advisable to go over the maximum load specified by the manufacturer.