i dont know the exact model of the psu, so i cant say much(i dont know the brand either so i cant vouch much on that end as well) but the 6870 requires 2 6 pin connectors, so it will consume a decent amount of power.
the 6870 i looked at on newegg requires to 2 6 pin pcie connectors. If you have the connectors you should be fine. Its a good card for only $170. The 6850 only uses 1 pcie connector. I read reviews on your psu and they are not good. Try those cards at your own risk but a good psu from antec, corsair or seasonic would be a wise move. For example:
I can't find anything about that power supply. Do you have a link to it? I have the feeling it's junk.
AMD recommends a 450w PSU for a HD 6850 and a 500w PSU for an HD 6870. If you had a quality power supply you can get by with much less than that but those recommendations assume a generic brand power supply.
Ibuypower is probably junk. They use the cheapest parts they can get away with. I can't think of a single quality manufacturer that makes an oddball 480w power supply. Unless you pay extra ( usually alot extra ) for a quality name brand power supply you are almost certainly getting generic junk.
and the psu came from ibuypower so i dont think its junk
It is junk. I just replaced my IBP's arctic power 480W PSU with a well reviewed CoolerMaster 600W. I've had the machine for a year, and from the beginning I have some random reboots -- but it was infrequent enough to be just annoying. 2 days ago it died spectacularly, and luckily it didn't damage anything else on its way out.