BTW, what's an AC or DC servo? There is only one servo, but I think you call AC servo a servo which has a drive connected to AC current and DC servo one which has a driver connected to DC current. The only actual difference is that in one case you have the rectifier built into the driver and in the other case you have it built into the PSU. Mine is called AC servo with integrated driver, which requires 20-50VDC, but it is still an AC servo and not a stepper.
DC servo is breushed DC motor with attached encoder for feedback.
AC servo is kind of 3 phase BLDC motor with encoder for feedback.

Drives for both types of servo motors could, by design, ve connected to AC or DC power source (at the end it is ALWAYS DC source).