How to answer? "Constant Voltage and Constant Current"

chip123

话题：How to answer? Thanks advanced.

one of my client asked me " What is the main different between "Constant Voltage and Constant Current"
If you know about that, Could you mind to tell me in english, thanks a lot !

for your reference
U=I.R
Constant voltage: the power supply works as a voltage-source.  when the load impedance changes, the output voltage keep constant.
And constant current, the power supply works as a current-source, when the load impedance changes, the output current keep constant