Solar panels use MC4 connectors. They are weatherproof, they lock together and they fit the thick, weatherproof cables used for solar power. They can handle fairly high voltage, but they can not be connected or disconnected under load though.
The Anderson Powerpole connectors are a good choice for DC power. I use Anderson PP30 connectors for most of my 13.8V stuff. They are robust and fairly small.
Most electronic devices will just rectify AC into DC before stepping it down with a switch mode power supply since that's smaller, lighter, and cheaper than using a mains frequency transformer. It's pretty rare to find a mains frequency transformer in consumer electronic equipment today.