A simple 9 Volt 2 amp power supply using a single IC regulator.
This is very simple circuit. Everything is done by the regulator. The 78S09 can provide up to 2 amps continuous output while maintaining a low noise and very nicely regulated supply.
The schematic will work with no extra parts, however for reverse polarity protection a 1N5400 diode is provided within the input, additional smoothing being supplied by C1. The output stage includes C2 for extra filtering, if driving a logic circuit over a 100nF capacitor is also desirable to reduce any kind of high frequency switching noise.