I summed it up as being the CPU ~ $200
MoBo $60
RAM $40
GPU $240
CASE $60
PSU $70 (ish)
OS: $99
~~ I got around $769 ~~ All in all yes, you could get a better Power Supply and the one they offered in the deal is WAY overkill. If you did already purchase it, if the Power Supply isn't already DOA I'd plan on replacing it anyways. I rounded everything up, so it's around $700 for all those parts. You're going to have to spend an extra $60 for another power supply, except this one will be a good quality Power Supply, and you'll be saving like $100. Next time buy it yourself, you know what you're buying instead asking if it's good.
NOTE: I rounded and guessed for all parts (not saying I'm really off on the dollar signs, I'm pretty sure I'm close on the numbers). Best of luck!