Passively reading some articles and this is a bit late, but all the comments above about just turning on the "Start After a Power Failure" option are missing something crucial.
This function ONLY works if the Mac loses power unexpectedly. If you have it connected to a UPS (as you should) and it does a normal shutdown... it does NOT power back on when AC is resumed. Even if you have a UPS that lets you set it to power off after the device is shutdown, Mac's just simply do NOT power back up. They are less of a, "Resume after power restoration" setting as they are a "Resume to Last State" setting. And if that last state was shutdown, that's how they stay.
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This function ONLY works if the Mac loses power unexpectedly. If you have it connected to a UPS (as you should) and it does a normal shutdown... it does NOT power back on when AC is resumed. Even if you have a UPS that lets you set it to power off after the device is shutdown, Mac's just simply do NOT power back up. They are less of a, "Resume after power restoration" setting as they are a "Resume to Last State" setting. And if that last state was shutdown, that's how they stay.