what the heck?

I actually bought this one by mistake.  I thought it was a dual charger for the USB charging cables but one port is smaller of the two larger- that I assumed were the full sized USB ports, just different charging capabilities.  There are three usb ports a regular 5V/2A (regular USB), DC/2A (this one is a slightly smaller USB), and a 5V/1A (micro usb port).  I can not understand why there is this DC/2A port.   I would've contacted the seller but there was no documentation in the box it came in.  There is also the wording on the listing that says...."