It doesn't take much. Like if you put 12 volts across a little electrolytic rated at 10 volts, WATCH OUT! The tranquility of your workshop could soon be very suddenly disturbed. Even with the proper polarity, they will BLOW-UP. The MAGIC SMOKE will be EXPLOSIVELY RELEASED. BOOM!
And speaking of capacitors, Rogier PA1ZZ sends this:
But don't blow these ones up. Some of them are 75 dollars a pop!