Official WIFI Shield + Uno rev2 -- no power from external adaptor

I am attempting to use the official WIFI shield with a rev2 Uno board to detect simple changes in the vibrations of a motor in-use. I can demo this functionality successfully using the demo code available at -- but only if connected to my laptop via USB.

Plugging the Uno into external power will power the Uno, but not the Wifi shield (no lights on the shield, no signal sent out, no power across board). The power sources I've tried have been as follows:

  • 9v 650mA
  • 4.5v 1A
  • 6v 1A
  • 9v 1A
  • 12v 1A

Is there a known issue with the wifi shield + external power supply? Power via USB is being supplied and my data is successfully sent to the datalogging service (cosm).

Many thanks!