When I do a Dell 9020 with Libreboot, any variant, I replace every fan with quieter Noctua fans which are premium quality designed in Austria - by comparison, the stock Dell fans are cheap, loud Chinese design.
Dell uses a non-standard connector, electrically compatible with regular PWM standard.
Adapters are available, but add greatly to cost and cable length, so I chop the old cable and solder it. Double-insulated; each wire insulated then all together, with heatshrink.
Here are photos:
I also do it for PSU fans, replacing the default one with a quieter Noctua fan.
The rest of the hardware in these machines is solid after replacing the RAM (I install new 32GB RAM, with 4x 8GB, and upgrade the SSD). I also de-lid the CPU and use quality liquid metal inside; and good MX-6 thermal paste outside it for the big cooler.
I use the best fans. Noctua are really really good. *Most* repair shops don't replace *power supply* fans. But I do!
Here are 2 photos, of different 9020 SFF PSUs:
Leah Rowe ist kein Roweboter