dual monitor setup for dell xps 9500

oh well that explains a lot! Quite annoying that they still recommand this one to order however there are new versions available, and ask 80 euros for it. Thanks a lot for your answer!

@sebastiaanM  I agree, and in my opinion even the newer ones are overpriced compared to the competition, but I guess that isn't unique to Dell.  First-party accessories are almost always more expensive.  I personally use this product, which I find contains a better port selection for my needs.  I don't care about VGA and DisplayPort outputs through these types of dongles, and that hub I just linked supports USB 3.1 Gen 2 (10 Gbps) even on its USB-A ports, which is unusual.  It also can take advantage of source systems that support DisplayPort 1.4/HBR3 over USB-C, and in that case its HDMI output can run 4K 60 Hz, whereas most adapters like this are limited to 4K 30 Hz.  And even though it's not mentioned in the documentation, I've confirmed that it can actually run 4K 60 Hz HDR.  Unfortunately the XPS 15 9500 only supports DisplayPort 1.2/HBR2 over USB-C, so you'd be limited to 4K 30 Hz or 1440p 60 Hz.  But it's still a solid adapter.  The only caution I'll throw out here is that you should NOT use its USB-C power passthrough port with that system.  The XPS 15 9500 with an NVIDIA GPU is designed for a 130W power source.  That is above the 100W max of the official USB PD spec.  Dell did something proprietary to stretch the spec to 130W, but that won't be supported on third party products.  And this adapter when connected to an external power source skims 15W off the source for itself before passing through the remainder to the system, so that can cause "Low power USB charger" warnings as well.  The workaround for that is to use a USB-C power source that supplies more than the exact wattage required by your laptop, but that isn't an option when using a laptop like yours that already requires more than the spec even officially allows.

To add to the comments already shared. From my first hand experience I have a Dell XPS 9500 i7 10750H with 1650ti. I am able to connect my laptop with a USBC to DP 1.4 rated cable to the DP on a LG 27GN750 FHD 240Hz monitor. And with viewing the Windows gamer FPS counter and the NVIDIA FPS counters my machine is able to maintain the 240Hz and HDR settings. I as well have used a LG 27GL850B QHD 1440p 144Hz monitor with the same connection and have been able to maintain HDR 10 bit 1440p resolution at 120Hz set in display settings. And have been able to maintain non-HDR 8bit 1440p resolution at 144Hz with no trouble. 

The USB-C to DP cable used - Plugable USB C to DisplayPort Adapter - 6ft (1.8m) Adapter Cable (Supports Resolutions up to 4K at 60Hz) found on Amazon as of 4/23/2021

Another solution I have used is combine the DP cable included with the LG monitors and attach to a USB-C to DP (female) adaptor- tomtoc USB-C to DisplayPort 1.4 Adapter 4K 60/120Hz, Aluminum USB 3.1 Type-C/Thunderbolt 3 to DisplayPort -- found on Amazon as of 4/23/2021