External Boot Drive USB-C Cord Issue?

[Quankus]

2017 27" iMac
4.2 GHz Intel Core i7 running Sierra 10.12.6
2 TB Fusion Drive with 32GB of Ram

After reading this thread (https://forums.macrumors.com/threads/2017-imac-27-external-ssd-as-boot-drive.2096033/) I was inspired to boot my slow iMac from an external SSD. I bought a Samsung 860 EVO 2TB and cloned my OS to it. When I try to boot from it the startup screen loads completely but never advances to the desktop, it just hangs there for hours. Initially, I thought the cloned OS might be corrupt so I ran a fix in Disk Utility which repaired some errors and gave me the green checkmark. It still would not advance to the desktop. Decided to try a a different USB-C cable and voila, loaded right up. The OS and files were all there but the speed was NOT. My friend's cable was an Apple USB-C charging cable with only USB 2.0 speed, not a viable solution to get the speed improvement I am after. I bought a second USB-C cord thinking the one that came with my hard drive enclosure must be junk but once again the start up screen just hangs with the new one. Do I need an Apple brand Thunderbolt cord to achieve startup and desired speed? I realize the speed of thunderbolt will be bottlenecked by the SATA drive. Could this be a power issue? Any advice is appreciated!

Hard drive enclosure and cable #1: https://www.amazon.com/gp/product/B071V4ZH59/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Cable #2: https://www.amazon.com/gp/product/B07D7RZ1VS/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1

Friend's apple charging cord: https://support.apple.com/en-us/HT201700#usbc

 

[Fishrrman]

1. Boot from your INTERNAL drive for the moment
2. Connect the external SSD/enclosure
3. Download the FREE "blackmagic speed test" app from the App Store
4. Run blackmagic on the external SSD
5. Post the results here so that we can see them.

A 2.5" SATA SSD mounted in a USB3 enclosure that supports UASP should give you reads in the 420-430MBps range.

 

[Quankus]

Thanks for your reply, Fishrrman. Your posts in the thread I linked to above were really helpful to understand the process up to here.

Here's where we are so far using the amazon basics cord:

 

[Fishrrman]

Something is very wrong if all you're getting are the numbers in reply 3 above.

I'd suggest you order ANOTHER 2.5" enclosure.
MAKE SURE it's advertised to be "USB3 with UASP support".

 

[Quankus]

Thanks for your suggestion. I've ordered another enclosure with USB-C to USB-C cord. And contacted the original enclosure seller and they are sending me a replacement.

I tried it again with the original cord and got these numbers and then the program froze, spinning wheel and then the drive was ejected. Very bizarre.