Using an OWC Thunderbolt 3 Dock installed permanently in my Mercedes Sprinter photography adventure van, I started connecting things. I realized with pleasure that I could cable everything into the Dock, even the keyboard and mouse, at least if I can fix-down the keyboard and mouse while driving so they don’t go flying off the desk.
Then I need plug in only two things to the iMac 5K: power cable and Thunderbolt 3 cable.
Shown below, the Mini DisplayPort cable for the NEC PA302W wide gamut display is near the left, a charging cable for flashlights (green) is on a USB port at right the keyboard next to it, an XQD card reader next to that, and a cable for the iPhone next to that. And there is still a high power USB port on the front of the unit and an SD card reader. Plus the USB ports on the iMac itself. The headphone jack... well I’ll just blast the built-in stereo system.
Slick setup, it seems to me. That 12V socket is for other stuff and is unrelated to the Dock.
The image below is a testament to the atrocious quality of the iPhone 7 Plus camera—worse than any 10-year-old point and shoot camera. And it is at ISO 30 here! So awful.