i bought a plug for my PSR-600 at Radio Shack. It's the plug itself. Just take the supplied DC pwer cable and slip the two ends into the plug by an easy press of an indention with a pencil.
Certainly they can't be the same plug because the 600 uses 13.8 volts while the 500 uses around 6 volts, however, the 600 cable comes with the scanner.
The PSR-600 would need something like this Radio Shack adaptor, although I dont know which adaptaplug fits the 600. Universal 12VDC Power Cord
Model: 27-1594 | Catalog #: 270-1594