Getting UPS Power from One Room to Another
You need an inlet in Room A, not an outlet



You'll need an outlet box with an inlet in it in Room A so that you can plug the output of the UPS into it with a proper cord (read: if you have to do weird crap to your cord to plug the output of the UPS into the wall, stop, because that's a sign you're doing it wrong!).  From there, you can use a suitable chapter 3 wiring method (assuming the crawlspace is not wet, NM/Romex will do; use UF aka "outdoor Romex" instead if it is wet/damp, though) to connect the inlet box in Room A to an ordinary box+receptacle in Room B.