On my Asus A8N32-SLI with an AMD64 3700+, 2x1GB Corsair XMS, an ATI X1900XTX and a XFi Sound Card (cheapest one )... peripherals include 2x76GB Raptors and 2x250GB Hitachi as well as a Lite-On DVD/RW... lots of fans 12cm and 8cm.
Now all of this is powered by my Thermaltake TWV550... and the little Total Watts Viewer ( TWV..gay ) shows me 84W right now... even running 3dMark2005 (score 10426) which rapes components it will not exceed 190W !!! Is this unit faulty ??? Or could my PC run on 300W ???
I hear guys saying they have to upgrade to a 650W PSU because they use 2 GTX's... or is oc'ing a major factor in the Required Watts Market ? I don't clock... rather spend the extra penny these days. When money wasn't so good I ran my XP1700+ at 2400+ ...she is still running to date - old faithful
Assuming the TWV is accurate (no reason I know of not to believe that) then your system would probably run on a 300w. As long as the 300w was good enough quality to handle it. I don't know how much juice an X1900XTX takes, but if it doesn't take much, then its probably accurate. One thing though - were you burning CD's & DVD's at the same time as your tests? That may change the total as well. Don't know how much however, as I've never thought about it.
OC'ing takes more power than stock, and having more than enough power means you have a PSU that isn't under stress so its more able to deliver stable power. Also, nVidia's GPUs take a lot of power - moreso than ATI generally.
Another thing; high end GPUs have a statement that says they need X watt PSU to run - usually 400 or so. To protect themselves, they have to assume that the consumer is running the most power-hungry CPU in existance, several power-hungry hard drives/other peripherals, and of course is using the cheapest crappy PSU they can find. Otherwise, it only takes 1 idiot consumer to win a multi-million $ lawsuit.
So, someone running a much less demanding system - A64 sips power compared to a Pentium D... - Can get by with less than the recommended wattage - until there's a problem. Then the techs can say get a powerful PSU, then we'll talk.
That's wierd. According to this and other places I have read, the X1900XTX by itself consumes around 120w to 140w. So, to me the total you are getting seems off, unless somehow all your other components put together only use like 30w, which doesn't add up.