Summary

AC Power IEC Standard C-14 Inlet Connector Snap-In R-301SN

This design is like all my other type of snap-in's.
They have to be recessed with a thin low tight fit with a border.
Outside of the border you can have your thicker normal walls.

Check out my older other one
Just a square. Because you can screw it in with hardware.
https://www.thingiverse.com/thing:4999545

Check out the 120VAC Outlet Holder
https://www.thingiverse.com/thing:4992409