Suitable for places with 120VAC wall power.

BOM

1. Honeywell AT150A1007 Transformer with 120V/208V/240V input
2. Taiss Universal Changeover Switch (4-position), LW26-20-4/2
3. AC Power Socket. Mine reads “AC-14-F1” and fits in a hole 27.5x47x1.2mm, but the closest I can find online is the LANGZMFG LZ-14-F3, which is about the same but requires a panel thickness of 1.0mm.
4. Banana plug pair
5. Shrouded female spade crimp terminals
6. 1.5ft or so of AWG14 wire or better
7. 4x M3x8 screws
8. 4x M3 washers

Principal of Operation

We take advantage of multiple inputs of the transformer to select output voltages other than the rated 24V of the transformer. If we feed 120VAC to the 240VAC input, we'll get half the rated output, 12VAC.

Instructions

Two versions included: V1 was printed and is what you see in the picture. It has some minor flaws, which are corrected in the untested V2. FreeCAD file (V2) is also attached for easy editing.

Slice and print on edge. You may need a manual support, indicated in red, if your bed adhesion isn't excellent.