It looks something like the old "medical" devices made to administer mild electric shocks sold towards the end of the 19th century.
Does it have two holes in the box for electrode wires?
This was my first thought too, the original TENS units. My brother has one he bought at auction. The quality of welding on the aluminum spool isn’t contemporary with the rest of the device. I’m guessing it was originally a hand-cranked generator of some sort that was repurposed, the magneto replaced with a spool to wind something up.
