OK sleuths, my solar is 2 x 85W in series thru MCB to Votronic controller, nominal 34.4V, actual 38 - 41V at controller. I then fitted power supply same as Robin to trickle charge 24V start batteries.
PS input connected from controller side of MCB thru blocking diode to PS input, 0V back to controller 0V.
PS output (set 27.0 to 27.3) thru fuse to 12V bus, 0V to 0V bus.
With PS connected to solar, current at MCB / PS drops to about 26.5V and PS output 24.2 rising slowly to 25.9 (battery not yet fully charged) and current varying (bad weather) from high of 1.0 to low of 0.1A.
If I pull the fuse (no output from PS) voltage at MCB pops back up to 38V or thereabouts.
No diode in PS output, it needs power from battery to operate.
I would expect current to be shared but voltage remain relatively constant