I don't know if that PSU is monitoring the fans and needs to read rpm values, that would make things a bit trickier if you remove them...
That's been addressed already. There is a software that would allow me to bypass the fan control system. I could also fake the RPM signal. Or even easier, leave a fast turning fan with the fins plucked out strictly to report RPM.
Bigger fans always moves more air making less noise at the same rpm.
Without testing, I am willing to bet a single 120 mm Gentle Typhoon fan spinning at 2150 RPM would push more air than the two small ones.
I don't understand the "block the holes" part, that would be like removing them but leaving obstructions to the air flow.
That idea might or might not work depending on how the PSU is configured. What I am talking about is removing the two small fans and blocking that hole with tape. Than I would install a 120 mm or 140 mm fan on the side of the PSU, not on the front where the two fans are. To do this, I would have to drill holes on the side panel of the PSU. But again, I would have to see the inside of the PSU to know if this can work. It would be dumb to install a fan on the side of the PSU box that blows air onto the back of a board, basically cooling nothing at all.
You will want to run it in "enhanced low power mode" or if Braiins OS gets ported, underclock it.
I don't think you get it. I am proposing to double the number of fans at slower speed, which would result in the same air flow. And I would also remove the front grill for better air flow.
In my years water cooling we did all sorts of tests to find out what works best. Often times we found out that two fans on a radiator, one pushing, and one pulling, will yield better results at 1000 rpm than a single fan pushing at 2000 rpm.
So if that applies here, I should be able to double the number of fans while greatly slowing the RPM for either same or better air flow.
And other way to get better performance with less RPM is to use thicker fans. Bitmain got it right when they decided to use 38mm thick fans instead of the standard 25mm ones. A 38mm thick fan will push more air than a 25mm one at the same RPM.