I want to use it to charge one of the inputs on my Aferiy P280 while driving, and connect a 400W solar panel to another input on the P280 for charging. Therefore, I also have questions about whethe...

P280 Support. With two XT90 input ports, it can simultaneously support in-vehicle charging and solar charging. However, given that the output voltage and current of vehicles and solar panels may differ, and some car batteries lack reverse-current protection, if the voltage and current from the solar panel exceed those of the car battery, reverse current flow may occur, potentially damaging the battery.

DC input power adjustment is not supported.