With this voltage regulator extension circuit you can increase the output current up to 10 A. T1 power transistor has a resistor in the emitter and thus the transistor’s current is proportional to the current delivered by the voltage regulator.
If the 78XX regulator and T1 are mounted on the same heat sink then the transistor is thermally protected. The output voltage is dependent only on the type of the voltage regulator used in the circuit. With the components presented in the schematic the maximum output current is 2 A. T1 is BD242 but for different values of the output current you need to replace some components (download the table at the end).
If higher values are necessary, some components must be changed according to the table presented in the excel file. For currents above 7 A then T1 must be replaced with 2 transistors (T1 and T1*) connected in parallel, each of them having a resistor in emitter, R1 and R1* respectively. Also the bridge rectifier is different.