So if it handles 3a @ 5v, does that mean it handles 3a at 20v? Or more? Or less? I'm thinking both carbon60 and I are wanting to run in excess of 60w / 20v@3a to make use of the large power supply capable of 20v @ 4.5a.5V@3A(5*3)=15W.. 15W@20V(15/20)=0.75A.. DC cabling meets amperage limits before voltage limits, usb-c's higher volts allows more wattage with same or less amps.
USB-C Socket Durability is an order of magnitude better than USB-A if built to spec.
I'd put more faith in the 20" panel mount extension posted being to spec than a $5 thing from eBay, but I'm mostly used to reading stories of USB C to USB C cables - never looked in to couplers.