Anything from a reputable brand. Wattage will depend on other components too. What do you currently have?
I honistly don't know, but i have ran a 660TI before?
If it could power the GTX 660 Ti, then it has more than enough power for the HD 7770. We still can't say if it's a quality PSU without knowing the model or brand. I just brought it up to make sure you had enough cables and power to run the card.