Electrolytic Capacitor Boom

There is a well-documented history of this sort of capacitor failing, both leaking and drying out, followed by a boom. The boom can include smoke, flames and shrapnel, whereas the leaking failure can cause corrosion on the PCB.

This first example is the boom after the device was reverse-biased when the wrong power supply was used.

The correct power supply was 12v center positive, and the one which was used was center negative; with no polarity protection, a boom is the result.