That port would be for passing the DC power to the SWiM module. The power supply is probably connected directly to the power port on SWiM16.
On the SWS-4 splitter the extreme left port says dor DC pass. What is ths port used for?
There is nothing connected to this port on my system.
If the power supply and the SWiM module aren't in the same location then you can connect it to the power pass port either on it's own or in line with a receiver to power the SWiM module.