So first question, i am currently running a Geforce 9800 GT EcoIntelligence (no 6pin connector required) on my 300 watt PSU that came with my PC, i've had it for a year and it is running flawlessly,and wanted to know if i HAVE TO upgrade my PSU before upgrading to a Radeon HD 5750 ???
Either/or, the above two choices would be an EXcellent replacement.
If Cost is important, go for the corsair 400 Watts - NO problem with up to 5770 1 Gig GPU. If you can spring for the extra then go with the corsair 450.
In any case, your system, when under Load, is to close to that 300 W max rating and as one poster said - Not the greatest of PSU. Save yourself some possible grief, the 30 -> 45 bucks spent on a EXCELLENT PSU is WORTH it and sleep better!