USB fails to power device?

[dukla2000]

One thing I am wondering is if there's a default setting for the USB 2.0 that's trying to mount the device rather than charge it? I guess that makes no sense.

Could be - but you should see noise in the system log then if the "presented" USB device is changing (dmesg or journalctl).

UPDATE: the device does say 5v 2A.

Most likely an absolute max that is theoretical and never reached. But does indicate >500mA very likely, and thinking back to your OP (boot, shutdown, repeat) does tend to say it is almost OK, gets to a point where it cant get enough power so shuts down ...

lsusb -v reports what power a USB device is limited to: I am sure a very crude measure on USB 2 ports but if you run the router on the USB 3 port then it may be a bit more useful. (My DVB stick in a USB2 port says 500mA - it is a USB2 device and so is clearly happy running somewhere under 500mA but no idea how much under. My Bluetooth dongle only asks for 100mA.)

But bottom line I figure you should use the power adapter.