Enabling AHCI mode over RAID or IDE

1. Run Command Prompt as Admin
2. Invoke a Safe Mode boot with the command: bcdedit /set {current} safeboot minimal
3. Restart the PC and enter your BIOS during bootup.
4. Change from IDE to AHCI mode then Save & Exit.
5. Windows 10 will launch in Safe Mode.
6. Right click the Window icon and select to run the Command Prompt in Admin mode from among the various options.
7. Cancel Safe Mode booting with the command: bcdedit /deletevalue {current} safeboot
8. Restart your PC once more and this time it will boot up normally but with AHCI mode activated.

https://www.dell.com/community/Linux-Developer-Systems/Dell-XPS-13-9350-November-2015-Install-Ubuntu-15-10/td-p/4683278/page/2