From that same framework desktop power supply deep dive blog post:
We spent several sessions inside of an acoustic chamber listening to and measuring different Delta fans to choose the one that sounded best while pushing both enough CFM and enough pressure to handle full load at high ambient temperature.
…
During low system load, the fan stays off, and once the threshold is passed, the fan gradually ramps to the target RPM.
To me it just sounds like a regular 40mm fan instantly going from 0% to 25-30% duty cycle for ~1min every ~10min. Mine doesn’t sound like a gradual ramp in person.
Noctua just posted a custom side panel: How to make the Framework Desktop run even quieter
The Nocrtua side panel does change the intake grill for the PSU fan, but probably won’t change PSU fan ramping behavior.