PSU Group Test: 500W, 600W, 700W, 850W

The Scores

There were several hundred measurements to analyse, but we made the process slightly easier by using the ATX spec as a guide (see table below). As the scores originally started life as a percentage in Custom PC magazine, we had to adjust the scores to fit into bit-tech's scoring system - they were rounded to the nearest 10 per cent after going through the scoring process described below.

The voltage stability tests take pride of place in the scores and account for 50 per cent of each PSU’s overall score. The scores show the number of test measurements that are within the limits of the ATX spec, converted into a percentage to allow PSUs with a different number of rails to be compared. Obviously, we recommend that you only buy a PSU that has perfect (100 per cent) stability.

The Features score includes the overall efficiency and PFC efficiency as measured in the 50 and 100 per cent load tests, plus the number, type and quality of the cables and how noisy the cooling fan(s) are at 100 per cent load. The Value score is a combination of the Stability and Features scores and the total output (in watts) divided by the price. These three scores added together give the PSU’s Overall score.

Feature Table