If it is a system that offers telephony service over coax, then there is a good possibility that there are taps on the distribution line that allow power to pass to the drop cables to power NIUs. AT&T Broadband was using this approach in the past. Not sure how much voltage would be allowed on the drop but I would guess upwards of 55V.
This is CABL.com posting #143215. Tiny Link: cabl.co/mLp5