I had a Q-Tec PSU once, a 500w (pah!)... It was OK powering my Athlon 750MHz and GeForce 4 Ti-4200, but as soon as I upgraded to an XP3200+ with a GeForce FX5950 Ultra, it couldn't supply the required power and my PC just kept re-booting.
I now spend a little more on my PSU's. I had an Antec, but that blew up and killed my DVD writer

and I've found that Jeantech supplies are good (even though they're from PC World lol)