The OM Series wall plug enclosure supports all types and sizes of North-American outlets, including standard center-screw and Decora-style, without putting any holes into the wall.
The backplate simply screws onto the outlet cover plate, then the top snaps over the backplate with any OM Series access point and 12v US power supply inside. This has the advantage of covering the mounting screw making it non-obvious how the unit is attached.
This enclosure must be installed on the bottom outlet. Replace the middle screw (standard) or bottom screw (decora) during install. It is not designed to cover both outlets.
The video below shows the installation process in detail.