If we assume two PS tracking each other in CV mode with the same CC limit setting and the load drawing different currents out of the two, nothing happens as long as both stay below the CC limit. When one reaches the limit, forcing the other supply into CC mode too, it would try to force the same higher current into its load, maybe damaging it. Or should the function be implemented in such way, that the lower current is tracked? But that would be two tracking current sources only, or did I get this wrong?
I have never seen tracking applied to the output currents of a bipolar output.
With the Tektronix PS503A, each current limit only applies to its side and the output voltage of both sides track a reference voltage. (1) So the two sides do not interact at all; it is just two power supplies permanently wired in series with one combined tracking voltage control, two individual voltage controls which set the maximum voltage of each side and the ratio between them, and two current controls. When tracking mode is not enabled, it is the same as if the tracking voltage control was set to maximum. (2) This way of operating may seem weird but it closely duplicates how some tracking regulators work in circuits.
In that EDN example where the outputs are balanced against each other, each sides tracks the other and current limiting on one side causes the voltage on that side to drop. The other side now tracks the *voltage* of the side which is being current limited so it also drops but it still uses its own current limit. The advantage of this over how the PS503A operates is that when the PS503A is used as a single 0 to 40 volt power supply, the lower current limit causes both outputs to drop simultaneously all the way down to 0 volts. With a PS503A, one side drops down to 0 volts (actually -0.6 from the protection diode across that output) and then the other side only drops if its current limit is exceeded. The disadvantage is that you might prefer only one output to lower its output voltage when current limiting occurs.
Which way is better? The balanced method will be better for maximizing power supply rejection in some circuits making it better as part of a built in power supply. The tracking method used by the PS503A is probably better for a bench power supply used for development and other work except in the case where it is being used as a single 0 to 40 volt output power supply.
(1) This allows the PS503A to be remote programmed.
(2) The way this works is that with tracking off, each output of the bipolar supply is set independently. Now when tracking is turned on, both outputs may be adjusted from 0 to the previous output voltage with the single tracking control and they always maintain the same ratio. This allows low voltage circuits to be powered without risk of applying a higher voltage during adjustment if only the tracking control is used.