The Empeg's wall wart can NOT be used

That sounds like a reasonable cause.

Yup. That's how I'm going to be remembered now. Great. Mr. Fire Marshal.

On the other hand, I ass-u-me-d that it was a 12v input and wasn't... well, backwards... when I plugged it in, and then walked away. So don't just blame yourself.

I still haven't sent the board back, I imagine it's thoroughly toasted anyway but I'll go grab one of those universal adapters that has a switch for polarity and try it tomorrow.. Every suitable brick I checked around here is negative shell.

If you don't plan on changing the boards (I'm sure that's expensive..) I think you should include a big fat warning in the package, maybe with directions on how to add the connector backwards.. Could be much worse if someone tests it on top of something flammable or expensive, or just sticks it in their car untested.