Don't buy those.
If you REALLY want an A-Power brand unit, look for them elsewhere, such as at
Geeks.com. They don't have any of the 600W right now, but they have up to 480W for $15. I recall them selling the A-Power 650W (or so) for probably around $25-30. I don't recall ever seeing any 800W units.
With that being said, don't buy those. I'm pretty sure I've seen A-Power units in person (probably a 450W or 550W) and it pretty much was a gutless wonder. Seriously, the innards were... almost empty. I can't see them putting out anywhere near what they claim on the label.