Xbox one power adapter wiring - converting it to a 12 volt power supply
Typically for Xbox related power supplies, you need to tie PS_ON to the 5V standby rail. You could do directly, but I would use a 1kΩ resistor just in case.

R-Sense normally indicates a Remote Sensing option for a power regulator. It would normally be connected at the far end of the power supply's connector, to compensate for any voltage droop from the cable. Considering this supply can pump 17 Amps down these cables, it can lead to a not-insignificant voltage droop. The internal regulator would then adjust the output voltage at the PCB so that it senses the voltage at the far end to be 12 Volts. Logic dictates it should be connected to the 12V input on your 3D printer's input. Use a multimeter to test the old connector for continuity on the R-Sense wire to 12V. You may need to cut the old connector open to make sure there is no diode or resistor needed there.