My Q-TEC (and do NOT confuse Q-TEC with "Qtechnology") had 6V on the -5V rail - tripped system alarms - and don't blame the monitoring chip, as it was ok with two other power supplies.

This was a 400 or 450W, can't remember - according to one test, the 550W model was a different design, and the only one they would come close to suggesting, lower models seemed to be the same base model with uprated heatsinks and stuff.