That is something new............I do not think I have seen that setting before.
In the power or boot menu I always see the "keep off / last state" option as regards to power outages.
Now I gotta do some reading.
This isn't even a particularly new motherboard (~6 years old). Maybe it's an Asus thing?
Getting a little off topic, this server build has resulted in some other interesting side adventures as well.
CMOS battery was dead (I normally check that when re-using old motherboards, but forgot to this time), so all my settings disappeared the first time I unplugged the PSU.
I learned that 3.5" HDDs typically draw a startup surge of around 20W (measured at the wall) when they first spin up. I decided to measure this to ensure I wouldn't be overloading the PSU (a 430W Corsair) during initial spinup of all the drives.
I installed an ATI Rage XL card (whoo-hoo, 20 year old tech!) in one of the legacy PCI slots to use as a console (no IGP on the M5A97), and discovered that although I was able to run the Ubuntu Server installer successfully, first boot into the new system resulted in a "signal out of range" message on the display. Turns out GRUB (and the Linux kernel) were defaulting to some video mode that the Rage XL and/or my old VGA LCD couldn't handle properly.
Had to do some Googling to figure out how to force it to text mode only; fortunately I'd had the foresight to install OpenSSH and configure the network as part of the initial installation, so I was able to remote in to the box to fix the display issue. The console display won't get used much once I'm done setting it up; this server will be running headless unless something breaks which prevents remote administration.
I also discovered that the Linux SMART tools have gotten a lot better about being able to pull diagnostic info from drives which are connected through a USB bridge. This used to be somewhat annoying in that you had to guess what sort of USB bridge chip you had, and specify it as a command line option; it seems to reliably auto-detect the bridge chip now.