I've been researching this and here are my thoughts. Just a hunch so don't take this as Gospel however at this stage I'm rather confident there's some serious design flaws with the Saturn retro PSU.
There's variations between Saturn models / stock PSUs, which I won't delve into here as I want to keep it relevant and simple:
Saturn (my version at least) has 5 power pins.
GND
GND
3.3V
5V
9V
The switch on the retro PSU toggles power on that third pin (3.3V in my list above) between either 3.3V or 5V. Some Saturn's have no 3.3V and two 5V rails, my particular Saturn console has one 3.3V and one 5V rail. So the switch ensures compatibility between hardware variations. It's wired as the middle pin as output, left pin 3.3V supply, right pin 5V supply, so pending on switch position one of those voltages gets sent through.
PROBLEM 1: The switch is only rated for 0.1 amps.
9V is used by the CD drive on my revision of Saturn. Later models ditched the 9V and just use 5V.
Not to complicate things, but some Saturn's do use 9V for scart but that doesn't apply here.
My hunch is the retro PSU designer neglected to account for Saturn's that utilise 9V for the CD drive, thus not enough current is available. Plenty on the 5V line, which is what the later rev Saturn's use, but this doesn't help people with earlier Saturn's that require more amps on the 9V line to drive the CD.
PROBLEM 2: The 9V regulator of the retro Saturn PSU is only rated for 0.15 amps maximim (with heat sinking).
Another thing worth noting, both the switch and the voltage regulator of the prototype version, shown working in promotional videos, differ greatly to the final released design. They definitely look more robust on the prototype. Coincidence or meaningful?
I'm thinking along the lines of him changing the design at the final stages for whatever reason (parts cost / availability / compactness etc) and never fully testing it due to the nature of what happened with things going south.
It may still work with ODE devices or later model Saturn's that don't use the 9V at all or as heavily, but as it stands if my assumptions are correct it's not going to work with earlier hardware revisions.