Oooh, no, that's one of the worst PSU-shaped objects out there:http://www.hardocp.com/article/2008/05/13/getting_best_buy_on_power_supply/8
concerns a smaller one, but also made by Huntkey. Then go to HardwareSecrets; other than a couple of more recent ones, I think they blew up every Huntkey they tested.
So, you might be able to get 250W out of it. You might run a HD7750 on it, but your best choice would be to get a real PSU. A 380W Antec Earthwatts would have no trouble powering a HD6850.