Where are you installing the 2nd drive ?  Bay 1 : nvme currently installed Bay 2 : ( since the nvme in bay 1, has been converted to U.2 or nvme use ONLY ) Bay 3 : sata Bay 4 : sata Please install the ssd or hdd using bay 3 and/or 4 
I recently bought a Dell 5820 with 256 NVMe class 40 SSD. I then bought a 3.5” 1 TB Barracuda Seagate HDD and after installing it, a flashing amber health light came on the 2nd SATA drive slot.  I returned the Barracuda drive and bought a 2.5” Samsung 860 EVO SSD; the same flashing amber light came on. I already tried reinstalling Windows with different BIOS settings and nothing works. What should I do? I already called Dell Technical Support and they tell me additional upgrades outside of Dell, i.e. the Samsung SSD, are not supported by them. Thanks!
Samsung 2.5” Amber Light Flashing