I'm trying to diagnose whether my computer has an ample power supply. Sometimes when I play a video-intensive game, both monitors lose the video signal, even though the computer remains on and sound playing. A theory I have is: the video card isn't getting sufficient power. I can't imagine it's overheating because the machine is well-ventilated and the video card isn't hot to touch when this happens.

Anyway, in my PC's BIOS there's a Hardware Monitor page, and among other voltages reported (such as CPU, DRAM, South Bridge, etc.) I can see the following values:

3.3V    3.152V
5V      4.944V
12V     11.872V

Are those the voltages used by peripherals? What voltage should I be referencing if I want to know what my video card (PCI Express) is consuming?

What is the normal range of values reported for those? My values above appear to be under by approximately 4.5%, 1.1%, and 1.1% respectively. Is that cause for concern?

How else should I be determining if my power supply is "right-sized" for my PC and video card, or am I perhaps barking up the wrong tree?