Gigabyte X299 BIOS setting - Power on after AC Power loss

How to automatically return of power from an AC power loss?

General Answer:
   Try this. Go to your BIOS Setting ->System & Security > System settings in the Control Panel > Advanced System Settings > Advanced Tab > Startup & Recovery Settings. 

For Gigabyte X299 Mainboard:
    Go to BIOS Setting -> Power management -> AC Back
    Set to "Always On"

http://download.gigabyte.asia/FileList/Manual/mb_manual_ga-x299-aorus-gaming-7_e.pdf