350W would do for 750 Ti unless its extremely low quality, how much Amperes does it give on 12V line? Look out for PSU in your case (either top or bottom) and check out the sticker with info about Amps on different lines like 12V, etc. Then check the max output (written somewhere around that) and mention that. I'm pretty sure the PSU would contain it, the card only uses 60W.