This is a simple adapter cable from bare wires to a barrel plug connector with 2.5mm inner diameter and 5.5mm outer diameter. The wires are red and black, with the red wire connected to the inner part of the barrel so it corresponds to a typical positive-inner configuration. Of course you can swap the wires if you need to use it for a positive-outer configuration — you just might want to label it in that case so you don't forget!
A typical, no-soldering-required usage for this cable would be in combination with the MIKROE-192 voltage regulator/rectifier when you need to power a 5V-only system with one of our universal power supplies (which don't have a 5V setting). Connect the wires from this cable to the 5V output screw terminals of the MIKROE-192, then plug your WA-VAR-US or WA-UNI power supply on a 9V or 12V setting into the MIKROE-192's barrel jack (polarity setting won't matter because of its diode bridge). Then you can connect this cable's barrel plug to your 5V system.