Wifi Rev 2 not working without USB connection

This is a repost of posting #632544 (very old), but is exactly same issue I am running into now.

What Works: I purchased 2 Arduino UNO WiFi Rev 2 units. The boards both work great when they are powered by the USB port. I am able to upload sketches and run them with ALL functionality including WiFi connectivity.

PROBLEM: However when I plug in any 9-12 volt supply and remove the USB connection, the UNO WiFi Rev 2 boards will not function. A Network scan shows they aren't even connected to the network. The green onboard power LED is on. Pressing the reset button does not change anything.

Anyone have any insight to this issue?

What is the rating of the power supply you are keeping secret?

9V battery connected via the barrel connector

That cannot deliver the current. That is why it is not working. THe PP3 can deliver around 250mA of power, your board uses 500mA - 1A when using WiFi

Yes, that's exactly what it was. Added a small switching supply (12V 3A) and it works. Thanks.

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