Apple uses a PCIe x2 SSD using NVMe. The Samsung 850 EVO is a M.2 SATA SSD drive and will not work in a NVMe based system.
You would need a Samsung 960 EVO which offers the needed NVMe interface. But, we still have a problem! As Apple's NVMe OS driver only supports their SSD.
Now the rub! In the Beta copy of MacOS High Sierra people have reported the new NVMe driver now allows 3rd party NVMe drives to work!
I my self have not tested this and Apple could pull support in the final released version of High Sierra so I wouldn't tempt fate here until the OS is officially released this fall. Lets see if the support is still present then.
Here's a good chart explaining the architecture of SATA Express & M.2
Confused! It's a mess! SATA Express was stillborn while you'll find logic boards with it very few drives offer it. M.2 is a different interface but leveraged the same architecture of SATAe just in a different connector.
IEEE did a better job within Ethernet's different PHY's. While it makes sense to have a common physical interface (M.2) and then use keys to define what the interface can support (device wise). This scheme is a failure! As the hardware & OS folks don't abide by the rules and oddball makers of adapters confuse have confused things even more.