The 650TX is more powerful than is necessary for 2 HD5770s.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