PC Apex have a new review up on the Cooler Master Real Power 550W SLI PSU

The fan's RPMs are controlled based on the PSU's load. According to the users manual, it does this by using a circuit that typically senses the temperature of an internal heat sink and/or incoming ambient air and adjusts the fan speed as necessary to keep and system component temperatures within specifications.

Cooler Master Real Power 550W SLI PSU Review