Why don't most lab power supply units display the maximum current?
Most bench power supplies, even most of the ones with the fancy digital meters on the front, are actually very simple internally. 

They are basically adjustable regulators, linear or SMPS, with a pot that adjust the output voltage, and another pot that sets the maximum current it will put out, plus a couple of standard meters that measure the voltage and current at the output.







simulate this circuit &ndash; Schematic created using CircuitLab

That is, when you adjust the voltage to 12V on the display, you are actually adjusting the output, and reading it on the meter, not setting the target voltage. Similarly, with the current limit, you are simply changing a resistor in some current limiter circuit somewhere in there. 

The point is, the meter has no idea what you have set. In fact, the meter often does not even have a one to one relationship between knob position and output values. They will hold the output at whatever values you set, but the values themselves are entirely operator controlled.

With better power supplies, you are actually telling some micro in there what voltages and currents you want to establish and it, with the aid of DACs and ADCs, controls the voltages and currents for you. Having that control gives those supplies the ability to show you what you have set. It is also why better power supplies cost more.