On Tue, 18 Dec 2018 08:10:50 -0500, "SC Tom" wrote:

"Char Jackson" wrote in message
.. .

[lots of snipping to leave just the relevant part]
I
connected a known working PSU (Corsair vx550w),
The PSU is
connected by the standard 24-pin connector and the 8-pin EPS12v
connector. The mobo has a separate 4-pin ATX12v connector, which remains
unconnected. ASRock tech support says that's fine.


I may have missed it somewhere in this thread, but have you tried plugging
in the 4-pin ATX12v connector? Certainly wouldn't hurt anything if not
needed, and would eliminate one more thing. Just a thought :-)

I know I wrote a word wall to start things off, but I wanted to be
complete. You're forgiven for having missed it in that mess.

This motherboard has both the 4-pin ATX12v connector and the 8-pin
EPS12v connector. My PSUs (plural) both have the 4+4-style connector, so
I combined them to make the 8-pin EPS12v connection.

BTW, as of this morning the new system is still humming along. No
unplanned, unscheduled shutdowns and restarts after raising the vcore
voltage last night. The light that I see is either the end of the tunnel
or an oncoming train, but so far so good.