This may be done in two ways. You may burn the capacitor up by turning up the voltage on the variable power supply. You will get smoke and some sparks but the capacitor will go nonconductive before it blows up. To blow the capacitor up in a dramatic way turn the voltage on the power supply up to about 120 volts, but leave the power switch off (This will be more reliable when the Variac is replace with the large isolation transformer).  When you turn the switch on the capacitor will blow up with a good bang.  You may then remove the smoke filled box and show the coiled innards of the deceased.