Hi,
Looking at the side power IN connector on the 9-Slot backplane it wires up:
+8V & GND -16V & GND +16V & GND
So you just need to pull off the GND and + or - as needed from each Mean-Well to the side connector.
From my sketch for the back end connector you would use:
RED & GREEN for the +8V
YELLOW & BLACK for the -15V
ORANGE & BLUE for the + 15V
I need to fix my sketch!
.