Most motherboards track voltages from the PSU.
If the voltage settings are within spec then your PSU is keeping up.
ASUS boards come with a voltage monitor and most PC testing tools have this ability.
Voltage sags of any of the legs can cause weired behavior - reboots - basically a unstable PC. Even if your PSU is "rated" for 650 watts doesn't mean it can't have a leg which voltage is out of spec even with the smallest of loads causing your machine to be very unstable.
This tool below is one of many free ones available.
Motherboard Monitor
http://www.snapfiles.com/get/mbm.htmlIf you find a better one please post it up.
