Most pre fitted PSUs tend to only come with a single fan. This fan is designed to exhaust the hot air from inside the case. Most of the aftermarket PSUs, (expensive), come with a second, ( intake), fan fitted underneath. This second fan can produce quite a dramatic improvement on system cooling. Here is how to add an intake fan to a PSU fitted with only a single exhaust fan"
FULL STORY @ BIT-TECH (http://www.bit-tech.net/?page=article&id=103)