power goes out, and then comes back on, do you want the computer to come on, stay off, or return to the last known state.
In the car, if you didnt have a smart DC-DC, and had it set to ON after power failure, and the power relay tripped by the accessory wire, it will start but from a cold boot every time, and it would pull the plug when the engine dies. Not shut down the PC, but yank out the cord.
So every time the key goes from off to on, the computer must cold boot because there is not power for Standby, and both hibernate and standby would require you to press a button to bring it out of that state. The BIOS settings only work for when it is a cold boot.