Our elliptical machine's wall-wart was sticking out far past the edge of the powerbar it was plugged into, and kept on falling out. This is a quick and dirty support for it. After printing, just zip-tie or duct tape the wall-wart to the enclosed squarish part.
It's customizable since it is unlikely your power bar and wall-wart will have the same sizes.
No supports needed. I printed in ABS with 50% infill for durability, but it was probably overkill.