I have just set mine up. I'm using a Dell server PSU and it's OC'd @ 400 and has been *very* stable for the last few hours. The best bit? I'm using some PCI-e cables left over from a Seasonic PSU and these have been soldered to the PSU output (though to do it again I'll use some sort of multiplug arrangement) anyway, the PSU was less than £10 delivered and is 750w. I'm still baffled why everyone has gone out and bought fancy pantsy PSU's.
So, if you're struggling for a high output PSU take a butchers for a server unit as these can come in incredibly high wattage units.
All together including the Antminer and the Dell PSU, it's considerably quieter than my 3mhs scrypt rig and consumes half the power.
Probably 2 reasons.
1. Not everyone knows how to solder the correct wires.
2. I have seen cheep dell server psus for $9 too. But im almost certain they are less than 80% efficient.
Pulling a 400 watt load 24/7 for a year would cost $50 more in electricty (@ 16 cents kw/hr for example) than a name brand Platinum unit. Say a Corsair platinum AX760 (7 year warranty) you can buy for $140, and you can power 2 Antminers, then you would save $100 a year.