Amateur radio benches and small repair shops rarely run one voltage: a handheld charges at 13.8 V, a router wants 12 V and a phone draws 5 V. JF20 is a switching supply that covers that spread without a pile of plug adapters.

Why would a bench supply need a 13.8 V preset?

Because 12 V nominal equipment is really designed for 13.8 V under load - the fixed position is what a radio actually wants, while the adjustable 5-15 VDC band handles the rest. Set the current limit anywhere up to 20 A, and the digital display shows volts and amps while the fan keeps the pass stage cool during long key-down sessions.

How far does one JF20 go when three loads need power?

Front USB supplies 5V/2A for phones and tablets, the cigarette outlet runs accessories up to 10 A, and the two 4 mm banana terminals carry the main 20 A output - a radio, a charger and a bench lamp can run concurrently, where separate wall supplies would need three sockets and three transformers.