12V 2A power supply for DC motor
You could get a 50HZ halogen lamp transformer that has a 12Vac output and is rated at 3 AMPs .These transformers have internal thermal protection so you have a good safe design basis.So you wont burn anything down .You should also fuse the primary and the secondary.Next place a bridge rectifier and a large electrolytic cap to make DC for your motor .Using PWM to run the motor is a good idea to get the voltage dead right .