A system includes a controller for automated test equipment (ATE) contactor to interface with a device under test (DUT) including a power converter having a primary and secondary side, each side has an input/output (I/O) pin. The controller causes the ATE contactor to apply a load current on the secondary side of the power converter at a first value and vary the load current to a second value. The contactor receives first and second indications, at the first and second load currents, of a voltage on the primary side I/O pin, a voltage on the primary side of the power converter, an input current on the primary side of the power converter, a voltage on the secondary side I/O pin, and a voltage on the secondary side of the power converter. The controller determines a primary and secondary side ATE contactor resistances based on the first and second indications.