I claim the ornamental design for an electric socket adapter, as shown and described.
FIG. 1 is a front perspective view of the electric socket adapter design;
FIG. 2 is a front elevational view of the electric socket adapter design;
FIG. 3 is a rear elevational view of the electric socket adapter design;
FIG. 4 is a top plan view of the electric socket adapter design;
FIG. 5 is a bottom plan view of the electric socket adapter design;
FIG. 6 is a right-side elevation view of the electric socket adapter design;
FIG. 7 is a left-side elevation view of the electric socket adapter design; and,
FIG. 8 is a rear perspective view of the electric socket adapter design.
In the drawings, the broken lines are for the purpose of illustrating portions of the electric socket adapter that forms no part of the claimed design.