And "industrial" electricity rates... 
Yes
bloody hell, two power plugs in the top machine? wow.
Haha I believe that is the SP35... 3.6Kw+ of power draw... two plugs are absolutely necessary
it's SP31, which is minimally more efficient than SP35
Yes, SP31 have more efficient than SP35. And Double PSU solution are in all YUKON SP3x devices.
Its brilliant because when one PSU goes down second will work and half of device will still hashing
only difference between the SP31 and SP35 is the PSUs. The SP35 has about 600W more available to it, which it uses to achieve about 600GH more. The SP31 is like running 4x SP20 units at 1.2TH, while the SP35 is like 4x1.35TH
Also of note, the power supply on the SP31 can handle 120 or 240v, while the SP35 needs 240v.