Last time, when I supplied 12 V from a power supply to the Arduino's 5V pin, it blew up. This time I'm going to use an adapter. Why does an adapter with a 12 V input not blow an Arduino up, as in the previous case? 

Or, should I have supplied 12 V to Vin pin, instead of the 5 V pin?

Edit: Sorry for saying 12V input, it is written 12V output and I meant a power adapter that is plugged into wall.