I’ve been hearing very good reviews about the Antec True Power 5.0 550W Power Supply. That’s the one I ended up going with even though I don’t have the GX2, I know it’s capable of providing more than enough power for it.
eVGA is safe. I’ve been running their 6600GT for 1.5 years in my main box without a problem. They’re not the flashiest company, but their products work fine, not to mention they’re usually on the lower end of the pricing spectrum.