Below are a couple of magnet chargers I have. The top row of photos shows a
recent acquisition with a 4 position ceramic switch - Off, Low, Medium, High.
The coil windings are a bit "loose", and it appears the enamel is thin and scratched on the outermost windings. Haven't yet cleaned it up and tried it. It's marked "12 - V" on the front edge of the left top pole plate.
The bottom row of pictures are of a charger I've had for about 20 years. It has most of the original box with a label and an instruction sheet. It DOES work. Maybe not the most powerful, but it will give a magnet a decent charge. The instructions indicate it will work on 6v "storage battery" or "110 volt DIRECT lighting circuit", with light bulbs in series to reduce voltage to the coils. The unit itself is in excellent condition, however, someone removed and bypassed the original push-button switch in years past. When you connect it, it's "on".
Click on a photo for a closer view. In some photos, I've left an ordinary item in the photo to give an indication as to size of the charger.