Solar charging cable plugs overheating

I have been plagued by overheating solar charging plugs. My 2 Delta 2 power stations (and Delta 2 extra battery) get sunlight energy from a 250 watt ecoflow rigid panel. It's wonderful to charge up 2 kwh of power over the course of a nice sunny summer day, and dump that energy into my Prius Prime.

The problem I'm having is that I'm cooking the input plugs of my Delta 2's. They should have no issues as the current I calculate with the wattage I'm seeing is well within the spec, nowhere near the maximum they are supposed to be able to handle. Yet, I have fried about 10 cables. Higher gauge extension cables don't help; the issue apparently is the plug, which gets hot and eventually melts the plastic, actually charging the plastic, melting glue in the plug, and in some cases, fusing the plug into the Delta 2's jack.

Has anyone else run into this issue?