The following circuit Diagram of (DUAL VOLTAGE POWER SUPPLY ) can be used for Misc.. application.
It requires a few components to built. The most important components of this circuit are REGULATORS.
1 : (AN) 7812 and 2 : (AN) 7912 AN7812 is the Positive Voltage Regulator. It regulates the voltage from (almost) 24vDC to 12vDC (accurate). AN7912 is the Negative Voltage Regulator.
It regulates the voltage from (almost) -24vDC to -12vDC. A transformer output must be between 12vAC to 24vAC @ 500mA. Input of transformer (Primary) should be about 110vAc-220vAC. It also include some capacitors to filter the current.
Source: Electronics Lab