According to AMD it requires a min 400w PSU but sometimes that is not the case. If you can look at your PSU and look for the numbers on it. It will look like this 12v 5v 3.3v it will show watts and amps like the total of the 3 I just showed you and it will tell you if you have two 12v rails.
If you can get me those numbers I will be able to tell you if that PSU will work. In most cases it will work but we have to make sure.
I agree with jaguarskx, the Dell PSU's are really actually decent, and the 5670 and 6670 are very power efficient. If it can run on some generic crappy PSU from HP (I've tried it), it should work better on a better Dell PSU.