Identify an Unusual USB Port

That is a port for a UPS Communications Cable Simple Signalling - USB to RJ45 cable for connecting to a computer. The cable is included with many compatible APC devices.

That is an APC cable by Schneider Electric cable P/N AP9827

https://www.amazon.com/APC-AP9827-USB-cable/dp/B0002WYJSU

It looks like half an Ethernet cable with just four wires in 1 3 5 6

APC's user manual from one type of UPS is downloadable at: http://www.apc.com/salestools/JGNY-9X784R/JGNY-9X784R_R0_EN.pdf

And an excerpt with that connector is: