This part is a kind of semiconductor called 78R12.

Function of this product has LOW DROPOUT VOLTAGE REGULATOR.

Manufacturers : UTC

Image and pinout :

Some of the text within the PDF file :

UNISONIC TECHNOLOGIES CO., LTD 78RXX LINEAR INTEGRATED CIRCUIT LOW DROPOUT VOLTAGE REGULATOR  DESCRIPTION As the UTC linear integrated LDO, the UTC 78RXX shows a high current, high accuracy, and specially low-dropout voltage. The features are: maximum 500mV dropout voltage, very low ground current. Cause the series have been designed for high current loads, so they are also used in lower current, extremely low dropout-critical systems (in which their tiny dropout voltage and ground current values are important attributes).  FEATURES * IOUT=1A ; VOUT=1.5V, 1.8V, 3.3V, 5V, 6V, 9V, 12V (Typ) * With ADJ version * Internal overcurrent protection, internal thermal shutdown * Internal overvoltage protection, internal short-circuit protection * Output disable function 1 1 1 1 TO-220B TO [ ... ]

78R12 PDF Datasheet Download