1500X won't charge if both DC to DC and Power Supply plugged in

Is this normal? I have the 1500X installed in my trailer, and have a DC to DC charger plugged into the barrel connector under the 'lid'. No power is being supplied to it (It is powered through the 7 pin connector, and it is not plugged in). If I also plug in the AC adapter that came with it in the front barrel connector, I get nothing. I have to unplug the one under the lid even though there is no power to it.

Is that normal? If so, what combinations of power can I use. Can I do solar and the DC to DC?