I’ve seen the (voltage) advantages of the buck/boost with the Pi Pico. The input voltage is so flexible and can be lower than the microcontroller’s 3.3V and it all still works well. I think the chip they use is lower current than the buck one on the Microrack power module at the moment.
The electrical specification also has
Voltage tolerance: ±10% on all power rails
For the +5V rail that’s 4.5V to 5.5V. For my measured examples even a good quality PSU like the 15W Raspberry Pi one (5.1V, 3A) can’t conform to that specification with an 8 module load - I measured 4.46V on the +5V rail.
When I first started using Microrack I was using my desktop’s type A USB (blue USB3) which can provide about 1.5A. That measures just 3.67V (I have a few more measurements in step 3) which I was blissfully unaware of. Everything seemed to work okay but it’s way out of spec, there’s likely to be further drop from schottky protection diode, any 3.3V regulators might have too much drop, perhaps some ICs won’t like it and it’s starting to get close to Vf for any white/blue LEDs. If people design their own modules to the Electrical Specification then these may not work okay.
I just took a look the midi→cv schematic and it looks like +5V goes into schottky diode then AMS1117-3.3 for the module’s 3.3V when the local USB isn’t powered. With 3.67V that’s perhaps -0.25V and then -1.1V (typ.) = 2.32V.
Issues could be invisible for anyone developing modules and testing them only using 12V via USB-C (or power jack).
I think it’s worth soliciting more views on this and in the meantime adding some recommendations for good PSUs and ones to avoid in the documentation.