To get a better overview and to illustrate the valid voltage combinations that's possible when using more then on DC source in series.
And as an example the use of a 10W LED constant current driver and PC PSU's to driver more then 1 LED with the same driver.
But note the PC PSU use 14 watt at idle so it only make sense if there is a heavy draw 100 watt per PSU or so.
All LED drivers lose 5-15W per 100W, the ones in my 10W LED flood light looks like those that has a 85% efficiency, so using many of them
also has a price. ~1W per driver.
The color codes should points to the right reference GND to use with the right PSU and voltage.
Since we are interested in the highest voltage it's the +12 & GND thats connected between the PSU's
In the example used they both run on +36V one of them could use +29V by being connected to +5V on PSU 3, if that voltage was required.
Besides the "main" power source(PSU3) using this as a external power station there is a lot of voltage possibilities to take from:
+5V(PSU1,2,3) to the temperature displays and such(USB). +12V(PSU1,2,3) to the fan controller. +12V(PSU1,2,3) to DC to DC constant current drivers,
like the ones used in MR16 12V LED spots.