This power supply build based on the application note of the LM317 of National Semiconductor .
Some features:

• Adjustable from 1.2V – 25 V
• Current output 1.5 Amp
• Short circuit proof
• Thermally protected

Other features as adjustable current limit, starting a 0 Volt, higher output voltage and higher output current are possible too: see the LM317 specification.source

Here is a simple circuit which can provide an adjustable voltage source of 0 to 330 Volt.The supply is short-circuit proof: the current is limited to about 100mA.source

It is a simple circuit regulated power supply, based on the known LM723, that drive a transistor 2N3055. The regulation of voltage, of expense becomes with potentiometer from 0v-30v DC roughly.source

This is a reverse engineered circuit diagram from an expensive commercial variable lab power supply. The unit is designed around an ordinary op-amp and easy to obtain parts. Although the unit uses a single transformer with two output windings the circuit works equally well using a big transformer and a little transformer. The test point at pin 8 of the op-amp goes high when the variable power supply is operating in current limited mode and it could be used to drive an LED. source