l do not quite understand what ''full power'' means, are normal rigs only using half power? Or does it refer to the tested car?

1. Power Output
We check the ability of the PSU to deliver DC power from 40W all the way up to full rated power. At each power level, the balance of loads on each voltage line is kept proportional to the maximum ratings of each of the lines at full power. Both the voltages & the current in every line r manually measured to ensure accuracy.

2. Efficiency
The AC/DC conversion efficiency is the ratio of DC output power to AC input power, expressed in percentage, with 100% being perfect. It is calculated for each power point; typically it is lowest at very low load, best around 50~80% of rated capacity, & a bit lower at maximum load. If a PSU requires an input of 400W in AC to deliver 300W in DC voltages, then it has an efficiency of 75%, at this point, & 25% of the power is lost as heat within the power supply.

3. Voltage Regulation
It is the ability of the power supply to hold each voltage rail (or line) at the required 12V, 5V or 3.3V under a wide variety of conditions. Standard requirements r ±5%, but many quality PSUs do much better. VR is checked at every power test we perform, from 40W all the way to full power, during crossload tests, & during low VAC input tests.

4. Power Factor
Power factor is the ratio of real power to apparent power. It is a difficult concept to summarize because power factor touches on many complex concepts such as alternating current, phase, reactive & resistive loads, etc. There r many detailed explanations of PF on the web, some of which will be linked in the reference pages of this article. PF has nothing to do with the DC output, & everything to do with the way the power supply handles the AC input. The higher the PF, the ''easier'' it is for the utility to deliver ''real'' power'' demanded by the power supply. The best PF is 1.0. Power factor can be corrected passively, for typical values of 0.7~0.8. Active PF correction usually leads to near-perfect PF, typically >0.95. Better PF does mean lower energy consumption from the point of view of the utility, but not high AC/DC efficiency, which is an entirely different matter. We measure PF at every power output level.

5. Low Load
We check the power consumption of the power supply on standby (unit power switch on, plugged into AC). The results r of interest to anyone who cares about energy efficiency. We also check power demand with the unit turned on without any load, a condition that can cause problems for some high efficiency power supplies.

6. Ripple (new for V4 PSU test system)
It is the amount of alternating current (AC) that appears in the DC output lines. A switch-mode converter, the type used in all PC power supplies, tends to generate a significant amount of ripple voltage. Many PSU specs express ripple as a percentage; typically it is <1%. On the 12V line, this means <120mV; on 5V, it means <50mV. Very low ripple usually indicates a higher quality power supply. Higher than normal ripple can cause instability with some components. Ripple is measured & expressed in mV on all the voltage lines at every load. Screen capture images of the waveform may also be shown.

7. Low AC Input Voltage (new for V4 PSU test system)
Blackouts may be relatively rare in most areas of the developed world, but brownouts r much more common. Brownouts r periods of low voltage in utility lines that can cause lights to dim & equipment to fail. Also known as voltage sags, this is the most common AC power problem, accounting for up to 87% of all power disturbances. The severity, frequency & duration of voltage sags vary. PC power supplies r designed to continue working with some variance in AC voltage input, but just how well they perform under low VAC conditions is not well known. Certainly, intermittent, frequent voltage sags could affect PC stability; a PSU that does not handle low VAC well could be the source of mysterious computer instabilities that some of users face.

We now test PSUs with 110, 100, & 90 VAC input at 75% of rated power. The 75% load is about the highest power load that a PSU is likely to be see, as most builders factor in some overload headroom. It is a tough test, especially at <100VAC input, when the AC current will increase proportionately to maintain the same DC output power. A PSU that can handle 75% load well with low VAC will certainly do fine at lower loads. We monitor all AC & DC parameters as the VAC is lowered. A 0~140 VAC variac rated for 20A is used to control AC input voltage to the PSU in these tests.

8. Crossloading (new for V4 PSU test system)
Our power load testing follows standard industry protocol used by most organizations such as Intel, the 80 Plus program & the power supply manufacturers themselves. It is a proportionate load testing. In other words, the load placed on the various voltage lines at 90W or 200W total DC output is proportionate to the maximum ratings of eac