[Dr. Dyno]

Not to be rude, and I'm open to getting humbled but those ports are exactly as they are labeled:
Top is 12V: 12 volt battery power.
Bottom is AUX: Feeds audio signal to your radio.

Yeah, I thought it would be obvious from the labels.
I don't use the Aux audio input but my BIL connects his phone into it. He complained about a whining noise. I think he bought some kind of a filter to eliminate it.