The ornamental design for the portable power supply for jump starting a vehicle, as shown and described.
FIG. 1 is a view in side elevation from a side of the device.
FIG. 2 is a view in side elevation from the front of the device.
FIG. 3 is a view in side elevation from the side of the device opposite to that shown in FIG. 1.
FIG. 4 is a view in side elevation from the back of the device, opposite to that shown in FIG. 3.
FIG. 5 is a top plan view of the device.
FIG. 6 is a bottom plan view of the device; and,
FIG. 7 is a perspective view of the device.
The dashed line depiction of the clamp and cable is merely to show their storage arrangement on the device, but forms no part of the design sought to be patented.