The same circuit can be used for a negative output power supply (figure 4) by changing the transistor to a PNP and reversing the polarity of the zener diode and capacitor. But that is not all that has been reversed, we add 0.6 volts so a zener of 11.4 volts will give us about a negative 12 volts on the output. A similar gain PNP transistor will again boost current output based on its DC current gain.
For a PNP we can use a TIP42 (TO-220, hfe = 15-75, 40 volts, 65 watts) or Mj2955 (TO-3, 100 volts, 15 amps, hfe = 20). In both examples we must not exceed the current, power, and voltage ratings of the transistors. Make sure they are properly heat-sinked.
The output power is also limited by the input power, both voltage and current. If the input supply to the regulator circuit is limited to say 1.0 amp, the total power out to a load will be a little less than an amp.