To test this, I unplugged the servo cable (3 wires, black wire closest to the edge of the “Home” module). When I plugged the USB cable back in, there was a green light on. With the power supply plugged in, the blue pen lift motor didn’t move this time.
I went back into Inkscape, and pulled up Manual Control, went into Enable XY Control. When I hit Apply, the low voltage warning came up.
I tried to walk the carriage in either X or Y directions, but only got the low voltage warning. It didn’t actually move.