"Molex brand 19045-30"
Jutht ath I suthpethed... Some call them a "Punch Down Box." Really a sketchy design, but I guess the amazing part is how many of them DON'T fail.
As I said, usually the failure is somewhere between inconvenient and perplexing. Providentially, your failure could have been far worse. It got nipped in the but, or at least just starting to blossom into tragedy.
My failed connection was from circuit breaker in a box (not an outlet) that powered the water heater. When I got it apart, I saw that it had lost contact and the white Neutral Wire was scorched along with that terminal in the speed box. I was just glad to find our water heater failure was where I could easily fix it. The fix? I gutted the speed box and used it to house connections made like in our house: Stripped, Twisted Together, Wire Nutted. And for the RV, also Tape Wrapped.