burning smell from power adapter (arduino uno and motorshield and 2 power source

Hello,

I am using arduino motorshield with arduino uno r3 in a project.
I have powered arduion uno board with 6 rechargeable double a nimh batteries. and connected the motorshield to a variable ac to dc power adapter (set to 9v) to control a 6-12v dc motor to spin for few second, stop and spin in reverse direction. I used this code to control the dc motor. the problem is after 5 minutes there was a burning smell from my variable power adapter and it was extremely hot.
was there something wrong with my wiring or was I supposed to use some kind of jumper since I am using 2 source of power...
I would appreciate your feedback..
Thanks.

void setup() {

//Setup Channel A
pinMode(12, OUTPUT); //Initiates Motor Channel A pin
pinMode(9, OUTPUT); //Initiates Brake Channel A pin

}

void loop(){

//forward @ full speed
digitalWrite(12, HIGH); //Establishes forward direction of Channel A
digitalWrite(9, LOW); //Disengage the Brake for Channel A
analogWrite(3, 255); //Spins the motor on Channel A at full speed

delay(8500);

digitalWrite(9, HIGH); //Eengage the Brake for Channel A

delay(2500);

//backward @ half speed
digitalWrite(12, LOW); //Establishes backward direction of Channel A
digitalWrite(9, LOW); //Disengage the Brake for Channel A
analogWrite(3, 255); //Spins the motor on Channel A at half speed

delay(8500);

digitalWrite(9, HIGH); //Eengage the Brake for Channel A

delay(2500);

}

Sounds like your motor requires more power than your adapter can supply, what is the current rating (Amps or milliAmps)?
And your motor current?

I have to check on that. But I didn't know if the motor requires more power it can burn the power adapter.
The other thing I noticed was although I was feeding the motorshield controller with 9v the output was maximum 5 volt. I am not sure if there's a limiting voltage thing with the motorshield controller or..

Thanks.