A super easy method to show what unit a transmitter is powering.
It is very hard to know what unit a power transmitter is sending power to once you have set one up, and you have lots of transmitters.
All you need to do is drag the transmitter target register into the building’s “store” register. This will send any items in the building into the unit, so I recommend making dedicated transmitter buildings that don’t use their storage. The 1×1 Medium slot building is the cheapest medium slot available.
Now, you should be able to see the line tracing the transmitter to the unit it is powering. If you cannot, cycle through the register display modes, the default key being TAB.