I made a non-CNC foam wire-cutter using a small transformer and a standard light dimmer switch. I can't remember the specs of the transformer, but I think it was just a doorbell type transformer. It worked well, but was only used with a 60" stainless steel cutting wire. The dimmer switch controlled the input to the transformer and allowed adjusting the temperature of the wire. Since the output of the transformer can't exceed the transformer rated output, which is considered "low voltage" it is pretty safe.