Here is a circuit diagram for a very simple but also very effective design for a PSU using LM723 and with an effective output of 0V as well as current limitation (0 to whatever maximum current you have the unit designed for)..
I recently dug up a PSU that I made during my student years and am now refurbishing: instead of an analog display of current and voltage I am incorporating a digital LCD display and a AT168 controller for both display and control functions (short circuit and temperature control).
I had a look around on the net to see if there were any similar designs but all I found were complicated designs using all sorts of zeners, transistors etc to try to get 0V output.
Therefor I decided to draw this circuit from the PCB on which I currently have it (I do not have the original drawing any more) and publish it here for your review.