What is the problem?
Pi Support reports low voltage on startup due to printer (Wanhao I3 Plus) being turned off but USB cable to RPI 3 still plugged in
What did you already try to solve it?
New official adapter which triggered the same error, If printer is turned on when RPI rebooted then error is not there, Printer can be turned back off after Ocotpi boot.
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...) 1.3.10, Wanaho I3 Plus