Recently, I bought XPS 9550 as my second laptop for video editing and gaming. As I tried to update GPU driver to the latest version, every game started becoming laggy and all the BGM or sound effect started cracking within few minutes. Although the problem can be solved as reinstall the driver from Dell support, the version of driver was too old to compatible with new games and software. e.g. Battlefield 1 required at least Nvidia driver version 372.70. Please provide with at least one update and fix the video issue in late 2016.
Current version on Dell Support
Release Date: 26 Nov 2015
Latest Version on Nvidia website
Release Date: 28 Oct 2016
Video lag and cracking sound issue can be found in the video below.
The Drivers that you see on the Nvidia Website are the latest drivers available for the Nvidia GTX960M. Since the most graphics chipsets are custom designed for the computer, the version available on the Nvidia website may not be compatible/ tested on the system yet as they provide a generic driver update for that specific chipset.
As to when the Dell website will be updated with a the latest tested and compatible driver, is hard to say as this involves through testing to make sure, customer's don't experience unforeseen glitches. But have you updated the system firmware and the chipset drivers to the latest version and patched the game with the latest updates.