The ornamental design for the electrical plug adapter, as shown and described.
FIG. 1 is a top side perspective view of an electrical plug adapter of the present invention;
FIG. 2 is a bottom side perspective view of the electrical plug adapter;
FIG. 3 is a top side view of the electrical plug adapter;
FIG. 4 is a bottom side view of the electrical plug adapter;
FIG. 5 is a right side view of the electrical plug adapter;
FIG. 6 is a left side view of the electrical plug adapter;
FIG. 7 is a front side view of the electrical plug adapter; and,
FIG. 8 is a back side view of the electrical plug adapter.
The broken lines illustrate portions of the electrical plug adapter that form no part of the claimed design. The solid lines of a light line weight illustrate surface contours and form no part of the electrical plug adapter.