The XLR->USB converters on the other hand do have step-up circuits to generate +48V phantom power. Post a picture of the circuit to be sure. I would guess the FET is running off the +5VDC USB rail, which means no step-up converter to generate a polarization voltage for an externally biased capsule. That is a 16mm electret capsule, so there is no polarization voltage. The FET is 2SK596, it is doing what FETs usually do in microphones-impedance conversion.
