The coin shrinker uses a flyback transformer and a full wave rectifier to store energy in high voltage capacitors, then discharge it suddenly into a coil of wire that is contained within a chamber. The coil is wrapped around a wooden dowel and coin or other objects. The machine connects to a normal 120-volt outlet and slowly charges the caps to between 12-16 kV in about 2-3 minutes. When charged, the power supply is disconnected, clamps between the charger and bus bars are removed, and nearby viewers are warned about the impending loud noise. When the primary switch is thrown with a long stick, the energy discharges through the coil which explodes from overheating and back EMF. Objects inside the coil are subjected to induction heating and a strong magnetic force when the current stops and the induced magnetic field collapses.

Various US coins with their before/after for comparison

Cart with four large, high voltage capacitors

Cart with power supply, full wave rectifier, and volt meter

Secondary/safing switch, a shim props up the ring and metal braid
Once the primary switch is shorted, the shim is knocked out the ring drips to short the bus bars

Left: door hinge for primary switch Right/center: anode and cathode and chamber

One of four HV capacitors

Remains of a coil of wire after discharge and safing
Blue painter's tape, green wire insulation, and copper 12-AWG wire

Scrap copper bits from the shrapnel in the chamber

https://www.youtube.com/watch?v=_MfjL-mePTg&t

https://en.wikipedia.org/wiki/Lenz%27s_law
https://en.wikipedia.org/wiki/Induction_heating