Thank you for providing very detail troubleshooting steps. Let me tell you that all those steps are exactly what I was going to tell to do in this case but did it already. Something you could be missing is testing another AC adapter.
You can also contact our support for a possible replacement:
I just tried it with another AC adapter (same voltage, amperage and plug connections)
But sadly the same thing happened.
I guess I'll contact support now
Is your media center linuxbased?
Did you try to put your NUC into sleepmode and from there it refuse to boot up no matter if you unplug the PSU?
Then it sounds like the case many other NUC users experienced and Intel has still not fixed :-(
Yep - was running openelec (which is linux-based)
I hadn't put the device into sleepmode - had just done an init 6 from the OS