It’s important to remember that you are not allowed to specify both the voltage across the load and the current through it simultaneously. As tooki points out, you can set the limits on each, but only one will govern (depending on the load). Typical bench supplies “stabilize” the voltage accurately, but “limit” the current (for safety, etc.) less accurately. A good lab supply can have similar accuracy and stability on both channels, often with indicator lights to tell you which channel is governing (CV or CC). Specialized lab supplies are designed for use as “constant current” units, with a less-accurate setting on the compliance voltage (again, needed for safety of the load or operator). LEDs need a constant-current drive, since if you apply a constant voltage, the current will increase as the LED heats up, and it may “run away” to destruction. With a constant current, the voltage across an LED will decrease, so there is no thermal runaway.