Arduino Mega and Arduino GSM shield 2 on top

Hardware Arduino GSM Shield
1

Hello, I connected the mega to 12v at the external PS connector and a big red component aside a button of the GSM board exploded. Anyone knows what it is and what the cause could be.

Screen Shot 01-23-18 at 10.41 PM.JPG

2

Nobody has a diagram or a boardview of it?

3

nobody knows?