Hi,
I had that happen when demnstrating to Amateur Radio class, power supplies,
AC == Transformer== Rectifier==Smoothing Cap oops, didn't check peak voltage.
While drawing on blackboard, remember them, RB Cap "bang" shot to the ceiling, where it collapsed like a concertina.
Lots of aluminium and paper and smoke.
Next time I taught it, I carefully calculated peak voltage so it would do it again.
I didn't say why I had a small perspex shield in place.
Still scared the chalk out of my hand.
Its surprising what equations and circuits are remembered when things go bang?
Tom.... :o :o :o
PS, I wasn't around when this went BANG.
A repair job at work.