To circumnavigate the power issue, the following procedure worked for me:
1. 2 x USB cables are required for this
a. 1 x USB cable for connection to the DC port. This is just for power, like from a USB hub, power adaptor, or similar
b. 1 x USB cable for connection to the OTG port. This is for the data transfer or communication
2. While holding reset button, insert USB cable for power into the DC port (blue internal light comes on).
3. Release the reset switch after about 3 seconds.
4. Connect the USB cable for communication to the OTG port on the MK802IIIS and USB port on computer.
5. Wait for device to be recognised (which should be instantaneous, so not too much waiting actually), update USB drivers (if necessary)
6. Install/restore/update firmware (or whatever)
My logic? To put the device into recovery mode, requires only for the reset button to be depressed, whilst powering up. Connecting the USB/OTG cable is only for comms between mini PC and host. I initiated recovery mode with a dedicated supply, and then continued with the rest.
During the firmware update process, the current supply required by the mini PC increases because of the internals coming alive. Making sure there's enough juice available to successfully complete the procedure is imperative. So even after you've successfully hooked up your mini PC to your host, the update procedure will inadvertently increase the current demand.
With that said, I've seen lots of queries regarding reboot looping, bricking, etc. on the forums. Maybe its exactly why those devices are showing those symptoms after updates. But then again....maybe its not....
Either/or, hope this helps....