First off, *all* power supplies should have what this one has.
A high current diode across the output jacks, cathode or banded end to positive. This is to protect the output from reverse voltage.
A high current diode across the 2N3055 pass transistor, cathode or banded end towards the collector. This protects the transistor from reverse voltage.
Both these diodes must be rated at more than the power supply’s maximum current.
Notice the output jacks have a capacitor across them. This should also have a 0.1 uF ceramic disk in parallel.