Hi i ordered it yesterday from eBay seller who said tested it's working. I have r9 290x which need around 350w and power full modular 750w with separate 4 gpu cables. I tried every possible combinations but I'm getting next message:

"please power down and connect the pcie power."

With 290x it's working fine but not with rtx 1080. Both are with water cooling 

Any suggestions please. Thank you in advance 

Kind regards Zlatko