In the meantime I managed to finally upgrade the PSU in the Jonsbo N1 NAS box. I got hold of a Silverstone SX700 which is a decent SFX PSU that provides up to 700W power (which is enough to provide power to all 7 drives in the system which I plan to eventually have).
View attachment 554731
I've run into issues with macOS getting wonky with external NVMe after an incremental clone.
Then it got weird with an internal clone, where the access grinds to a halt.
By sheer luck of goofing around, I connected the problem to APFS snapshots on the clone target.
I suspect there's a macOS bug with APFS snapshots.
What I'd been seeing if Clone targets with snapshots (CCC enables default in later releases) will unpredictably hang when incrementally updated.
And for external drive (e.g. USB) once the pathology sets the drive may hang on any write. Worse, it may corrupt the clone if you try deleting its snapshots.
Try disabling APFS snapshots on the clone target before making any clone.
Source snapshots are ok.
For internal targets, the pathology is less severe, but incremental clone operations may slow to a crawl. Disabling and deleting snapshots on internal target can overcome the hangup.
This story is based on my direct experience from a few days ago.
* * *
Regarding 700W for 7 drives that need 7-10W each, you've mosdef got enough power!
I've got 14 spinners in a box with with a 5Ghz all-core 11900K running all out inc a 6600XT plus trimmings all on a Corsair RM650x with no power issues. So i figure your 7 drives are well covered.