What happens if I connect a low voltage rated capacitor to a high voltage?
A literal answer is this:



There are three blown capacitors; two can be seen as spirals of grey material still reasonably in situ, the third is nothing more than the base and the internal terminals. They were all rated for 6.3V but, do to a failure in the power regulator, they were connected to a whopping 7.5V. A negligible amount, so one would think, but the outer can of that third capacitor blew off with such force that it punched a hole in a piece of 3mm plastic - about 80mm away - and embedded itself into a battery on the other side.

All that brown stuff is a fibrous material similar to cardboard, and it gets everywhere. I don't know if there's some kind of oil inside the capacitor that dries when it is exposed to air but I do know that it sticks like glue to whatever it lands on.