Dell has just released a new Realtek HD Audio driver version for the XPS 9520 & Precision 5570 laptops - v6.0.9430.1 A25 (released on Thanksgiving November 24)
Windows 10: Once windows installed it automatically installs "Realtek® Audio" driver ver. 6.0.9285.1. It does not matter where you move the volume slider it always plays sound at 100% volume and it's very loud. Using Dell Command Update I upgraded audio driver to the latest available version 6.0.9369.1. I am able to choose volume I want, but when I select 100% it play sounds at 50% of volume it was before I updated the driver. And it's really quiet. Uninstalling the latest driver gives 100% of loudness again without any options to choose less volume. Installing back the latest driver gives 50% loudness when slider moved to 100%. If I slide volume to 50% I barely hear sounds. Windows 11: With default driver after windows was installed the sound is quiet. After using Dell Command Update I upgraded audio driver to the latest available version 6.0.9369.1 and it becomes a bit louder, but not that as it should be. For example, if you run dell UEFI diagnostics it plays sounds very loud. I read through [URL] so, I believe, there should be an .inf file section which describes min and max voltage or idk.  Who knows how to fix it?
XPS 9520 Sound volume too low