Update for anyone with new BIOS (I have 1.20) or an XPS 9560/similar: DellFanCmd / DellFanKeepAlive seem to intermittently work. Meaning sometimes the EC control takes over despite this software trying to disable it. But other times, DellFanCmd is able to take over and actually reduces the fan speeds to the specified setting. It seemed that using the internal GPU for all software helps reduce fan speeds, but the system still seems to randomly speed up my fans, even when I'm not using the high performance GPU or even doing any computations at all. It's quite annoying. I may downgrade the BIOS soon and try DellFanCmd again if this can't be fixed.