There's a few factors here, and many of them point at the possibility of damaging your motherboard if you arn't sure what you're doing. You don't seem to, and this is a bad idea. You shouldn't be trying to boot a PC off a jerryrigged power supply without a good idea of what you're doing.
This is kinda anecdotal but I do suspect you might need some of the ...
Note that in the BIOS settings, under System status, it says "Not present" for the entry M.2/SATA Port 5, although there is definitely an M.2 drive present
Your new 970 EVO is an NVMe drive which connects through PCIe; it is not a SATA device and does not consume a SATA port. (Most M.2 slots are dual-purpose and accept both SATA and PCIe devices.)
No, there will be no additional stress on the system - most of these sensors are always reading and being acted on in the background anyway. Depending on the sensor I guess its possible that it will slow the system down a wee bit while it is gathering the data.
Is the warranty still active? If so call Dell at this point FOR SURE
WHEN the issue is happening I'd disconnect everything that isn't needed & try to power-on again. Have only the PSU connected to motherboard, CPU, 1x RAM stick. Disconnect: all external connections except for power cord, hard drives, PCIe/expansion cards, front panels, case fans, etc.
I have had a shutdown problem similar to this one you are having for the longest while.
Besides searching all over the web for answers and posting to specific or relevant OEM forums, I also reported it to bugzilla.kernel.org back in 12/2018:
Never had a reply.
Then again this year: