Glad I found this post as the manual that came with my EVGA 1080 FTW was not clear at all on power connections. It showed a diagram with supposedly acceptable connections, one with an 8 pin (6+2) going into just one of the two 8 pin power connections on the card, and the other with what suggested both power connections on the card with 6 pin connections on each.
When I tried to boot with just one 6+2 connection I also got the prompt to "power down and connect power supply", so I thought I'd plugged in the 6+2 into the wrong 8 pin connection on the card.
But, no, it actually needs BOTH power connections to be plugged in.
My new EVGA SuperNOVA 650 GS, 80+ GOLD 650W, Fully Modular, EVGA ECO Mode (the PSU was default internal switch to ECO mode - should I turn this off?) PSU came with plethora of cables, several VGA cables that had one single 8 pin connection on one side (obviously to go into one of the VGA ports on the PSU) and on the other end it has two chained 6+2 pin connectors. It seemed that this was designed to be plugged into both the 8 pin connector on the card and after doing this the system booted up.
I'm thinking it's OK to do this, the cable clearly seems designed for this purpose and I don't see any benefit of using a separate similar cable from the PSU to the second 8 pin connection on the card as that would leave two cables with unused 6+2 connections? Also, If and when I buy a second 1080 FTW card, I'll run out of PSU VGA connections as there's only 3 and if one card requires two too be used, then that's not going to work for two cards?
One other thing I'm confused of is the future potential of buying another card to SLI. The SLI connection cable that came with the card clearly uses one of the two 8 pin connections on the card to SLI to another card. So that would mean both cards would only be using one 8 pin power connection instead of the current two? I guess I'll cross that bridge when I come to it!
Now, just to find out how to OC this thing using my Gigabyte Z170X gaming MB! Since the card clearly needs both 8 pin connections to be plugged in to power up, it's obviously designed to OC! However, at the moment I can't see any game that really requires more GPU power, so maybe I'll hang off OC'ing until titles come out that I notice are starting to push the card.
Thanks for any and all replies.