Unless, I am wrong, some types of mics are passively powered (an output and a ground reference). ANd other mics are actively powered (an output, a ground reference, and a power)
Of course an electret mic needs a power supply for the jFET inside.
2-wire electret mics have the jFET as a common source amplifier.
3-wire electret mics have the jFET as a source-follower.