Arduino Uno external power supply stopped working.

I was uploading code to my arduino Uno R3 when I heard a pop and then a puff of smoke. Now the Arduino will not work with the 9VDC power adapter plugged in unless the USB is connected to the computer as well. When the 9VDC power supply either AC to DC adapter or battery the power light and "13" light flicker as if it's struggling to get power as soon as I connect the USB Cable to the computer and Aeduino the Arduino runs fine and stable.

Something blew, so the board is no longer reliable.

How did you connect the 9V ? to the barrel jack, or to Vin ?
When you connect an AC voltage to Vin, there will be popping and smoking.
The barrel jack is protected with a diode.
You can check the schematic : http://arduino.cc/en/Main/arduinoBoardUno

Do you have a good quality regulated 9V DC power supply ? If you don't, please get one. Before you blow the next Arduino board. There are very cheap dangerous power supplies, that can output maybe 15V or 20V without load.

Any specific reason to post an Arduino Uno problem in the Arduino Due forum? :~

I think a moderator should move this in the right place...

Ralf