The Schoeps Phantom Power Test Plug can be plugged into a microphone input or cable that carries 48V phantom power to verify that sufficient current is available to power a Schoeps microphone.
According to DIN EN 61938 standards, a 48V phantom-powered microphone draws a current of up to 10 mA per channel. The Schoeps CMC 5, CMC 6, and CCM microphones require only 4 mA or 5 mA if active accessories are used, so the PHS 48 Phantom Power Test Plug tests for approximately this amount of available current at the required voltage level.
To note, the PHS 48 Phantom Power Test Plug does not test whether the 2 feed resistors in the supply are sufficiently well matched to one another. If they are not well matched, any interference picked up in the cable can cause an increased noise level.