Q: Loses all power

Sometimes when you just turn the vehicle on it loses power. No rhyme or reason. Daily driver. Maybe happens 4 times out of 20 times turning it on.

For instance, this last time, wife turns on headlights (car not running). As shes walking to rear of vehicle, loses all power (headlights, dash, radio needs reset, etc). When she opened rear hatch everything comes back on. Thats just one example.

One time tried to unlock door with fob. Wouldn't work. Manually opened door, then worked fine.

So far hasn't happened when being driven.

Also, seems like sometimes you can see the dash lights slightly flickering when it's running.

Wondering if there is some sort of master relay that controls power to the vehicle.

My car has 204000 miles.
My car has an automatic transmission.