Just remove this monstrosity, install what is called an "old work" junction box, re-strip your wires, j-hook them around the screws, tighten, assemble, and install a new cover.
Just replace those boxes with one gang cut in boxes. They'll have those wings that tighten down when screwed in. This is needed if the box isn't against a stud. Looks like that box is similar. Then use regular 15 amp outlets or switches. Wire ground wire (bare or green wire) to green screw. Wire neutral (white) wire to silver screw. Wire hot (black, red, or blue) wire to brass screw, in that order. Before all this, disconnect the wires from old outlet in the reverse order after shutting off power to be safe. Regular switches will have two hots and a ground. Wire accordingly.