I've got a 500GB 2.5" SATA drive rescued from a dead notebook, that I'm using as an external drive in an "Orico" branded drive enclosure with USB-C port.  Transfer rates are pretty pathetic to two PCs, a 7th gen Nuc or a notebook, both with USB-C and USB-A 3.1 ports

The fastest transfer rate I've seen is about 50MB/s, about 10% of what the SSD is supposedly capable of (6Gb/s). 50MB/s is about the same as old 2.5" HDDs I use for backup. The drive enclosure came with a USB-C -> USB-A cable, that I'd have thunk should have been up to task, but on the other hand the drive enclosure - including that cable - cost less than outrageous retail prices of a quality cable alone. 

The only USB-C -> USB-C cable I've got is a "Cygnett" armoured 5A cable, that seems to work fine fast-charging all devices (phones etc) when plugged in to USB-C port on the NUC or notebook, but data transfer rates to the SSD are the same as when using the USB-C - USB-A cable.

So what's likely going on?  Is the (cheap) drive enclosure the bottleneck, or is it that none of the USB-C cables I've got up to the task for fast data transfer?  

Edit:  I found the drive enclosure on PBTech site: link

I now see this review:

Yes the enclosure has a USB-c port but fails to mention the cable supplied with it goes from USB-c to standard USB. So you need an adaptor to plug it into a USB-c port on a computer, which defeats the whole point of getting it in the first place.

My experience with what I'd have thought was a quality USB-C -> C cable makes me think it's worse than that, the enclosure probably has USB 2.0 guts in it - but wired up to a USB-C port.  My googling uncovers the same enclosures being sold on TM, claiming 6 Gb/s data transfer speed.  I think I've been done.