These machines do not have a "power supply", they do however have a thermal fuse that will trip if the machine overheats. You can find it under a metal clip on top of the boiler; on Step 8 of the Barista Teardown it's on the left side of the boiler directly above the water inlet, with a brown wire leading to it, inside a clear protective sleeve. You can test it by putting a voltmeter at either end of it's wires (with the machine unplugged!); if it's open then it has tripped and will need to be replaced, if there's continuity then it's fine and you have a different problem.