I had installed the latest bios (v28) as soon as I received my Nuc and I had power issues immediately. I never even tried the shipped bios.
I could only get the Nuc to power on by removing the ram, and reinserting it. It would boot once but a restart after that would make it fail. Removing any component caused this behaviour.
I ended up returning the Nuc to Amazon and my replacement works with no issue. I have not upgraded the bios yet as I cannot see why if it works.