You still have to plug in two wall wart style transformers (one is for reference voltage, the other is to power the box) into a real power outlet outside the box, and then get those wires inside the box. Or commit some electrical code sins and wire that inside the box too.
Many houses have a doorbell transformer mounted on their service panel with no plug; I can’t see how that’s a NEC violation (and therefore providing a path for a similarly engineered, code-compliant solution).
Yes, I have seen this, but it is unusual, and the doorbell transformer is still outputting AC, not DC, but at a lower voltage, and that output is not run inside the breakerbox.
How do you route them out of the box? Should the wires criss-cross? Bundle them?