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: