Still not right for all 3 in series - I assume your going to turn down the voltage on all 3 so they max at 83.x when in series?
It should be crossed again on the last unit, the ground i mean.. at one end (bottom of stack) pull GND (-) off as an output line then connect the + positive of that meanwell on the bottom to the GND (-) of the one above it, then the one above it gets it's + connected to the final unit's negative and you pull the + postivive charging lead off the last.
So you end up with all 3 in series and Ground coming from the bottom unit, VCC or Positive coming from the top unit.
The current will limit to approx 125% of whatever the S-350-27 would output so you need to do:
1.) Set desired (lowest) output voltage from the S-350-27
2.) Fan mod - replace thermistor with resistor so fan on S-350 comes on always
3.) Adjust current output via shunts or resistor R33 on the S-350-27
That should get you working reliably and quickly
Hope it helps!