@sdetweil OK but how would you wire both the controller board and the raspberry pi? Could you suggest the whole setup? So which power supply connected to where and where is the step down connected to?

Any idea how I could power a Raspberry Pi 3B (5.1V 2.5A) and a B173RW01 V5 controller (12V 3A or 5A) board (which powers a display) with only one power supply behind a magic mirror? The thing is that it has to be as flat as possible. Is there some kind of power supply and split cable for micro USB and 5.5mm x 2.5mm DC power connector and the different voltages I listed?

I could just use two power adapters/supplies but I only have one power outlet and I can’t fit a power socket behind the mirror :/