Too bad I don't have good enough PSU for a bunch of 1080ti. Thinking of going with server PSU for this case in addition to one regular one.
Someone was asking about dimensions for the Hewlett Packard 1500 watt common slot power supplies + X-adapter breakout boards. Conclusion: two of these will just barely fit back to back in this case but that means the cards in front of psu's will need to be GTX 1070's or smaller due to length restrictions.
Dimenstions with the X-adapter board attached: exactly 12 inches in length; width is 4 and 1/4 inches because the breakout board is just slightly wider than the HP 1500 psu itself; height is about 1 and 3/4 inches but that is deceptive because you have to allow for the insertion of your power cables, which can only bend so much.
Here are some photos which I hope make it clearer:
http://imgur.com/a/SEd2U
I'd like to mount the two PSUs horizontally, stacked; looks like it can be done with a spacer or bracket to raise the top PSU a couple inches, to give enough room for cables plugging into the breakout board. I think this way, it's easier to access power plug from the back.