Your PSU sounds like a cheap generic, however even if it is only good for half its label it should be enough.
If at all possible, get a GDDR5 version of the card. It need not have 2GB. For not much more money, a HD7750 (also a GDDR5 version) will also run on your PSU, and is a much stronger card. If this is for movies and video, not games, a HD6450 is cheaper and will suffice.