9V Voltage Inverter

From the vendor

This dinky little daughter board will allow you to easily convert any existing positive ground effects to (daisy chainable) negative ground.

De-solder the supply and ground wire from the existing board, and solder to this board, then take a couple of new wires from the -9V output and ground connections on this back to the de-soldered pads on the effects board.

Really handy, really small and a quick job – now your positive ground pedal will run from your isolated multi power supply, no need for an extra plug!