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I wouldn't be so sure. I think they can squeeze 2 TH/s out of 1100-1200W.
2000G * 0.7W/GH = 1400W MINIMUM...OK... 
The assumption is that the S4 works with underclocked/undervolted ASICS to reach a better W/GH ratio, I would assume somewhere between 0.55 and 0.65 W/GH, so one 1300/1400W power supply could indeed do. But of course we'll not know for sure till @BITMAIN reveals the exact specs.
Evga 1500w Platinum
and, btw...
5units of S3+ = 355w x 5 = 1,775W
i assume S4 will be around 1500w - 1700w
they wont waste chips like that..
they better selling chips like avalon do than planting so much undervolted chips
and sell it so damn cheap
they're not doing charity here buddy
You will get higher efficiency out of a server-class PSU, and even better if you're running on 240v instead of 120. Take a look at the SPTech specs for their servers, and do the math to see what they're pulling, and they're doing it at 90+ efficiency. The one thing I'll give SPTech is that they are built well, using (supposedly) higher end server grade parts.
By undervolting you achieve several different things. Yes, you lower your hashrate, but you also lower power draw significantly, lower heat generation, and raise efficiency which allow you to get higher numbers with much more stability. The ASIC chips themselves are cheap, they're only "wasting" a few bucks by having to add a few more when undervolted. Seriously an extra hashboard to them is probably $50, so when you're dealing with a $1000 server that's really not much at all.
