If you check the circuit, there are two sets of wires in parallel on the Molex plug, just single wires to the rear terminals. Both are fed from the same point. You could add wires in parallel to the terminals to increase the current carrying capacity of the wiring, although it might be the screw terminals that are only rated at 16A.
A 20A linear power supply is marginal in terms of powering a 13.8V 100W radio, many of which mention 23A or even 25A.
There doesn’t appear to be any over Voltage protection in the PS-50 either, so if the pass transistors fail your transceiver is toast.
Can you not sell it and buy a more rugged supply, and one with proper over Voltage protection? A NIB PS-50 would likely sell for enough to cover a better engined Astron PSU.
73 Dave