If you experience bad results from 5770 you should upgrade your PSU ...5770 needs minimal 500 watt PSU ... if you want to UPGARDE it i suggets you to go for CORSAIR 650 TX ... its great PSU ...but i dont think 5770 has any problem with your current PSU ...but if you want to get higher you realy should UPGARDE ur PSU
The 650TX is more powerful than is necessary for 2 HD5770s.
No, I'm just saying it isn't necessary. Also it wouldn't make the card run any better. As long as you are using a PSU that is sufficient then adding a more capable power supply will make no difference as to how well the card runs.