±12V Symmetric Power Supply by LM7812 and LM7912 Regulators

This circuit provides ±12V regulated DC output based on LM7812 and LM7912 that are National Semiconductors' two of the most popular positive and negative three terminal voltage regulators. The circuit is supported by a handfull of capacitors.
The transformer is a minimum 1A, 115VAC or 220VAC (depending your mains voltage) to 18VAC.
C3 and C4 are ceramic 50V capacitors and the other electrolytic capacitors are 35V.
The bridge rectifier is 100V and 1A.
Circuit operation is simple. The transformer reduces the mains voltage to 18VAC and then the bridge rectifier applies a full wave rectification to this AC transformer output. C1, C2, C3 and C4 stabilize and filter the rectified voltage. Regulators fix the voltage at +12V and -12V DC levels. And at the final step C5 and C6 capacitors stabilize the ±12V DC voltage.
Source: YMYA Electronic