The Test Regimen
After some careful consideration on potential approaches, our test regimen includes five non-variable load tests. Each of these power loads represents a class of modern gaming system, from a standard gaming system all the way through to a highly over-clocked top tier system with relative loads defined on each of the voltages. We had considered using simple percentage based PSU specific loads (20, 40, 60, 80 and 100%) equally spread across each of the voltages up to the maximum capacity, but unfortunately this does not represent any type of realistic load. So, instead of theoretical tests that do not reflect any type of real demand, we have instead defined the following five enthusiast class systems for testing.
Each defined system class will draw a defined wattage and amperage on each of the main voltage rails. You will notice that the 3.3 and 5 volt rails loads both stay relatively low compared to the 12 volt loads. This represents true power demands of a modern enthusiast system and helps explain why so many manufacturers focus on marketing the 12 volt capacity of the power supply.
Next, to round out these five standard system tests, we do a final test and load up the power supply with as much draw as possible per specification on the 12V rails to see how well the unit performs. We bring up the 3.3V and 5V loads a little more than the standard test to represent additional cooling and over-clocking along with an increase on the 12V rail(s) up to a maximum of about 76.5 amps. It would be hard to imagine any current system using too much more power considering the recent emphasis on reducing the power draw of peripherals.
In the case of multiple 12V rails, each is loaded with differing amperages to represent actual PC loads. The CPU draw is relatively constant and as you add more peripherals, especially graphics cards, the loading increments in large steps and does not load the 12V rails evenly. The following list represents the type and number of components represented by each of the system specific load tests.
What is the impact of this? - Let's say you were considering a four rail PSU to power your single GTX 280 system. It is then possible one of the 12V rails could potentially have no effective load. It will depend how the power supply manufacturer has designed the voltage distribution. To make sure you have the right information, each review will note this distribution. For example:
To allow for these PSU specific variations, each of the rails will be loaded uniquely to reflect an actual peripheral load from the class specific CPU, graphics card (one, two, and three), peripherals and cooling loads. If we had simply loaded all the rails evenly, the tests would not reflect an actual system load. If the power supply operates within specifications for a test class similar to your system configuration, you will be more confident that it will operate, as tested, in your actual system.