Dell Optiplex 3010 with latest Bios A12 (motherboard MS0520 or 042P49 A01 take your pick). GTX1070 card in PCI-E 16 slot, powered by 6 pin supplemental power from Upgraded PSU Corsair CS550M.
GPU- no fan spin, machine still booting using on board graphics, no message about using different card. I tried it without 6 pin power- nothing.
Bios doesn't seem to have a 'disable on board graphics' option, I have added various cards to other Dell machines and have never changed Bios before.
CS550M is not sufficient power. CS750M would be minimum recommended for GTX 1070. Why? Because the system needs 220W minimum and the Video Card needs 450W minimum. This is why booster power supplies are 450W.
Even with sufficient power however LEGACY CSM and Option Roms must be ON and SECURE BOOT OFF.
GTX 1080 in XPS 400
Bios settings are correct. Geforce docs say PSU min 500w. I tried powering ONLY the GPU using the 550w PSU, and the old PSU for everything else, no reaction from card.
If you connect a 6 pin power cable to a GPU that isn't plugged into a slot, should the GPU fans turn? I'm trying to think of a way to tell if card is dead. The GPU fans certainly don't move while seated in PCI slot and power turned on.