The Open Scan Pi controller board is powered by at 12V power supply in its barrel connector. In the standard design of the OpenScan hardware, the ringlight plugs into the controller board, not the Pi.
In fact, the Pi gets its 5V supply from the controller board, not from its MicroUSB connector, in the design.
You can use the controller board's 12V DC power supply for the ringlight to test it (or any other 12V supply on hand.
The controller board ringlight plug power is controlled by the attached Pi with the OpenScan software during normal operation.