The ornamental design for a flashlightpowersupply, as shown and described.
FIG. 1 is a perspective view of a flashlight power supply;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The design which is claimed is shown in solid lines in the drawings. The broken lines in the figures depict portions of the flashlight host that form no part of the claimed design.