ADATA XPG SX8200 Pro for Dell XPS 13 (9350)

@Hackkerszk  If you want to verify that your system is detecting an SSD, just go into the BIOS Setup after you install it and check the System Information/Summary section at the top of the list on the left.  In the information section on the right, scroll down to the information about storage devices.  If you see your SSD mentioned, then it's detected.

Dell defaults to shipping almost all of their laptops in RAID mode for a variety of reasons having to do with standardizing factory build processes and some historical situations.  I've written about this multiple times elsewhere on the forum, but basically, if you'll only have a single SSD that will NOT be an Intel Optane drive, then you should switch to AHCI, because RAID mode delivers no benefit, and since it enables the Intel Rapid Storage controller, it becomes one more driver you might have to deal with (although recent Win10 installers might have built-in support for the XPS 13 9350's Rapid Storage controller by now).  AHCI is also necessary if the vendor of your SSD offers an optional NVMe driver and you want to use it.  Samsung offers this type of driver, for example, but it's only available for retail Samsung drives, not OEM Samsung drives.  There likely won't be much of a performance difference either way, but AHCI is just simpler because it exposes the storage interface directly to the OS, rather than having the Rapid Storage controller enabled.

But if you're curious, since RAID mode enables the Rapid Storage controller, it can be useful in certain cases -- including setting up actual RAID, using Intel Optane drives (where RAID mode is required), using Intel Rapid Start or Intel Smart Response (both of which are used in systems with an HDD and a small SSD cache module), and using an NVMe drive with an OS that doesn't natively support NVMe (like Windows 7, where using RAID mode allowed that setup).  Since Dell currently sells or has sold laptops where at least one of those situations has applied, they standardize on RAID mode on almost all laptops they sell.  Standardizing makes things easier, there's no real performance difference, and the only downsides of RAID mode don't really apply to them.  Having to include one extra driver isn't a problem when they're already integrating a bunch of drivers in their factory build process anyway, and the inability to use NVMe drivers that are sometimes offered with retail drives doesn't matter to them because they're not installing retail NVMe drives at the factory.  The only big downside is that RAID mode doesn't allow you to use Linux, since Linux doesn't have an Intel RST driver built into its kernel.  But Dell doesn't offer very many systems with Linux pre-installed -- although the ones where they do, such as the XPS 13 Developer Edition, presumably come from the factory in AHCI mode.