Can a pwm dc fan speed be controlled with a voltage controller connected ONLY to neg. & pos. wires?

Modification of the controller itself was not the suggestion, so much as putting a few parts in between it and the powered device.

The XGC0384BX-1000U-A9H appears to be a 2-wire device, so no difference with the original material in question.

“3-wire” fans are typically one of three things:

  1. A fan that allows speed control via a logic-level (input) signal
  2. A fan that facilitates numeric measurement of speed through a logic level (output) signal
  3. A fan that gives a yes/no indication as to whether it has be hit by the #*%& and thus stopped completely, again via a logic level (output) signal.

The three controllers linked in your prior post appear designed to interface to the type (1) above, and unsuitable for control of 2-wire devices.

This post speaks to related topics, and may be of useful information.