I use a no name PSU on my PC at the moment and I can concur that the voltages are a bit off of what they should be.
I've used an Antec in the past. They are one of the better companies.
Just be careful of some of the companies that put their badge on a budget PSU.
If you have done the AT PSU mod, ATX is not that much different.
Double check things like: +5V vs -5V. I believe the 12V on ATX can put out a lot of amps so if you get something wrong, it will fry your motherboard.
I haven't modded for a while so can't help you atm. Ask some more questions here however...
