Check the power supply from the router to the UPS and ensure the ONU is receiving it properly.
Check the power supply from the router to the UPS and ensure the ONU is receiving it properly.
The 12V 2A splitter will provide the same amount of current to both devices. It won't reduce the voltage for either one.
On a 12V DC UPS they usually provide just one output since they’re built for individual devices. I own a compact wall-mount unit with a swappable 18650 LiPo battery, and there are also larger packs containing multiple cells—like the one I use for emergency LED strips. These can power devices for hours, whereas a standard inverter UPS might only run about ten minutes.