Why does dph3205 have 2 inputs?
To elaborate on what people have already said in the comments, it's not really two inputs; rather, it's one input with two connections to it.

There's a simple reason for doing this: Any connector is going to be rated for a certain amount of current, probably somewhere on the order of 5~10 A for a terminal block like that. If you want to have a 20 A input or output, it's often easier and cheaper to just use multiple contacts on your connector rather than get a larger (and more expensive) single connector. Likewise, wires have current ratings as well, and you might want to use two smaller wires rather than one larger one.

The two IN+ contacts are shorted together on the board, or possibly even inside the connector, so if you try to connect two different power supplies to them you'll be putting the power supplies in parallel. Unless your supplies are made for that and you know what you're doing, don't do that. Likewise for the IN-, OUT+, and OUT- contacts.