I was cleaning up my house the other day and found a cable, still wrapped in plastic. It’s black, has a standard flat USB plug on one end, and a plug that looks like an RJ45 on the other, but upon closer examination, has got 10 pins (5 connected) rather than 8 as on an RJ45. Anyone know?
Could be almost anything. Got a UPS with USB connectivity? UPSs often have RJ style connectors on them for some reason, even if the connection is serial or other.
Could be a UPS cable for hooking up the UPS to your computer. I got one in the last UPS I bought. It was exactly as you described, right down to the color. It came from a APC UPS.