I find out there are two micro USB connectors - one on short side next to SD card, one on long side next to SATA. I was using the one next to SD card
BTW: Swapping PSUs is absolutely useless if you don't take contact and cable resistance into account: cnx-software.com/2017/04/27/se…-boards-or-charge-phones/ (99% of all USB cables suck since power wires too thin)
Wrt 'read only filesystem': Your SD card is the culprit (quite common, even genuine ones die sooner or later). Do you use Etcher to flash the card or tools that don't do a verify?
Alles muß raus! Energieeffiziente OMV-Hardware-Schnäppchen auf eBay-Kleinanzeigen!