A lot of radios were battery powered back then using 22.5 and 45 Volts I think along with a giant 1.5V for the tube filaments.
According to a video I saw a doctor would take the Violet Ray device with him on house calls. For portability, you would have
to ask what was available at the time and it might have been one of those 22.5 volt radio batteries. But, who knows ?
Few people had electricity in their homes in the 1920's, especially rural areas, so the doctor couldn't just walk in and hunt for a wall receptacle
so it's doubtful that it was line powered.
A DC source sounds about right but at what value ?
More research needs to be done on your part.
I wouldn't hook it up to the AC line just yet.