We claim the ornamental design for a generator adaptor, as shown and described.
FIG. 1 is a rear perspective view of a generator adaptor showing our new design;
FIG. 2 is a front perspective view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a top plan view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines formed by dashes show unclaimed subject matter and form no part of the claimed design.