Total system power for 6570 (loaded running furmark) is 204 Watts (You will be lower).
Based on that a 350 Watt Tier 2 PSU would be fine.
However if Planning n say running two 6570's in xfire, or at a latter date updating to a better GPU a 450 watt tier 2 (Possibly a tier 3) would be an excellent choice.
44w for ddr3, 60w for gddr5. Depending on your other components you can run it on a good 200w. Though for most, a 300w will be required. Power requirements should be figured out with the specs of the system in question. Otherwise you're going to get guesstimates for your requirement.