The ornamental design for a powerstrip, substantially as shown and described.
FIG. 1 is a left front upper perspective view of the power strip;
FIG. 2 is a right back lower perspective view thereof;
FIG. 3 is a left elevation view thereof;
FIG. 4 is a right elevation view thereof;
FIG. 5 is an top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a front elevation view thereof; and,
FIG. 8 is a back elevation view thereof.
The broken lines in the drawings are for the purpose of illustrating environment and portions of the power strip that form no part of the claimed design.