Well that's very odd.

Perhaps the original PSU developed a fault and drew a surge, which set off the protector? You'd not expect the router to be damaged in that situation though. Did you then plug the same PSU into a non-protected source???

Well, yes, I did try to see if the power supply was still working by plugging directly into a wall socket and got exactly nothing. That was why I assumed it was the power supply that was borked (and hoped it was just the power supply). Sadly not however.

The router has just gone back to Draytek for them to look at it. so I'll see what they say.