I'm running Windows XP Pro using a Thermaltake Toughpower Qfan 750 watt power supply and in the bios it reports the 12 volt rail as 12 volts but in windows using CPUID's HWMonitor it says it's about 1.1 volts so either somethings wrong with my power supply/motherboard or HWMonitor does not report accurately in XP. I have had the power supply out of the pc a couple of times to test with a multimeter and it reads fine with a hard drive connected but maybe theres a quirk when under load and the 5 volts and 3.3 volts in HWMonitor are reported fine.