PSU cover for the typical 12V MW style power supply used on cheap 3d printers. You need 3 screws (probably already leftover in the kit of your printer).

There is an extra space for 220DET module: https://s.click.aliexpress.com/e/_dUBbk7f
to detect power loss (Marlin firmware feature)

The button and fuse combo used for this is: https://s.click.aliexpress.com/e/_d6ProLf

The cover should be glued in place. I don't like big bridges on printed pieces, that is why this was needed.