How is the 640 a cheapy?
Here
is a review for the 520C which is basically the same unit. Also apparently this is just a rebrand of the Season S12II platform, for which there is a review
hereI'll summarize for you:
Soldering job looks terrible. I've soldered more cleanly on protoype board than this unit.
Fails crossload test miserably. (Although unlikely to see such a situation while mining).
Doesn't come with power cable?
No OCP. If you accidentally draw too much power (an easy thing to do with only 620W available to you), bye bye MOSFETs.
I used the own the EA750, and it is a POS. It is expensive as hell and gives shitty ripple supression. I could load the unit so hard with an i7-920 and 2x GTX570 that the system would be unstable even though I was well short of the 750W limit. There are far better 750W PSUs than that one.