The power supply sounds okay and did you open it and take a look?I would say the outputs are gone.Any smoke from a amp can't mean good and the protection doesn't need to go on for it to be blown.The owner that had it before you could have had it modded or repaired before and than it could be anything.I would look for a new amp and not put to much more thought into it other than if you are going to sell it or get it fixed.Sorry about your loss.