I had been wanting to do this for long time and finally just decided to. I hooked up a Fluke ammeter to the input of my system to measure the total power consumption while running. I think most of us have no real clue how much power we are using. I know I didn't. Remember, the power supply is only about 80% efficient, so if the power consumption from the wall comes out to 500 watts, then the system is probably actually using 400 watts. Here's my system: Athlon XP 2000+ 1 gig DDR 3200 RAM SCSI card plus 3 SCSI drives GeForce4 MMX video CD burner DVD burner card reader 5 fans When I bought the system, I got an Antec 480 watt PS. When it went out, I replaced it with a Seasonic 400 watt fanless PS. Now it was acting weird, so I replaced that with a PC Power and Cooling 500 watt PS. With the two PS failures, I was getting concerned about how much power I am using. But when I measured the power, the maximum draw was 1.2 amps! Which works out to 144 watts from the wall, and that is about 115 watts available to the system. I ran it for a while and did a bunch of things trying to work the CPU and drives as much as possible, but that was the most power draw I could see. I did not do anything with the CD or DVD drives, but how much do they pull? Am I missing something? All this time I was thinking maybe 400 watts wouldn't be enough, but it looks like overkill.