Question X370 Gaming Pro Carbon: Power failed during BIOS flash to earlier version seems to have bricked the MB and blown the EVGA 850 GQ. Anything I can try?

Sep 30, 2019
I was flashing my MSI X370 gaming pro carbon MB back to an earlier version(after supplier couldn't get 3900x)mainly for the previous UI, and 3000 version was no longer necessary. At 25% of an incredibly slow USB 3 port bios flash, the power failed. Everything is surge protected. Before I turned back on I reset the bios(battery out, short jumpers). When turned back on - no POST, but RGBs, coolers, and case fans all powered up. CPU and RAM POST fail lights indicated they had issues. Swapped 2700X for 1600X(for if base version bios wasn't 2000 compatible) and swapped out the Corsair Vengeance LPX 3000 for standard Crucial DDR4. POST failed, still indicating CPU+RAM. Checked both seated right and continued to try differing amounts of RAM single and dual slots. Still no POST. Reset bios several more times, but nothing. So, I got a new B450 Aorus Pro set everything up - POST failed. In expensive exasperation I swapped out the EVGA 850 GQ PSU for and old 400W PSU non modular, that I knew was working. New board POST'd fine. Re-checked the X370 with a basic 1600X+Wraith Prism cooler, 16GB Standard RAM, 1060 GPU, 4TB Seagate HDD. No POST with 400W PSU. This lead me to conclude that not only had the X370 bricked, but the EVGA 850GQ had blown too, which is unusual. However, the EVGA PSU is still supplying power to the to the fans, RGB, and attempting to POST. If blown, this wouldn't happen as far as I know. Unless something specific to the CPU power module failed - beyond my knowledge. I bit the bullet and bought a ROG Thor 850(coz pretty and 10yr warranty). Tested the new PSU on the X370 1600X setup, and wont POST. Same POST failed CPU+RAM indicators. B450 2700X setup working fine. Can you think of anything I'm missing, or any advice other than RMA(RMA = I gave up)? Any help would be greatly appreciated.

Parts available:
MSI X370 Gaming Pro Carbon
Gigabyte B450 Aorus Pro
R5 1600X
R7 2700X
64gb DDR4 Vengeance LPX 3000
24gb DDR4 Crucial 2133
ROG Thor 850 PSU
Generic 400W PSU
Wraith Prism Cooler
Corsair 1001 Pro AIO
EGVA 1060 6gb GPU
MSI 1070 Aero + NZXT G12 Bracket + H100i v2 GPU + AIO
1tb Samsung 970 EVO nvme
4tb Seagate HDD

I would love to get the X370 and PSU working again, and build another Streaming PC for my daughter, with a decent upgrade path. But I'm truly baffled. My apologies if this was long winded, but I'm at the limit of my knowledge. I have been working with PCs and builds since the mid 90s, so fairly good base knowledge. But I'm flummoxed. Did the bios failed update harm the PSU, or did the Power fail short the PSU and fry the board.
Please help.
Sep 30, 2019
RMA what you can. Don't see why a BIOS flash or power failure would brick a PSU. You were mightily unlucky!!!
Cheers bud, but I wont admit defeat just yet lol. It may come to an RMA at some point. I just can't see how both would fail simultaneously other than a surge(which is protected against). I've had MBs brick before and wont even try to POST, and PSUs go, but it's usually dead, never partially dead. Gonna give it a couple of days and see if anything turns up.

PS like your rig, was hoping to get a 2080ti this year - that's gone out the window now lol. However, got enough dough left for the case I want: Lian Li ROG/Derbaur 011 Dynamic XL (out on the 8th Oct). My Corsair Carbide is a little too cramped for the AIOs, and Aerocool DS 230 is silent but not exactly good air-flow. New GPU's gonna have to wait.

Current rig is work related for audio/visual production(hence the AIOs)...but I end up gaming ;)
CPU 2700X + H100i Pro
MOBO Gigabyte Aorus B450 Pro
RAM 64GB 3000MHz DDR4, Corsair Vengeance LPX (4x16GB)
NVMe 1TB Samsung 970 EVO
GPU MSI GTX 1070 Aero OC + H100i v2
CASE Aerocool DS(Deep Silence) 230
HDD 4TB Seagate Barracuda + 2TB Seagate Firecuda
PSU ROG Thor 850W
PCIe Elgato 4K60 Pro
STUDO Line-6 HD 500X Modelling Pedal Board + Line-6 Spider IV 75W Modelling Amp + Line-6 Variax
Very odd situation, but seems like the power failure may have somehow damaged the PSU, surge protection or not. Not really seeing otherwise what could cause both to fail at the same time. Some power delivery works for fans, ect. The power to the VRMs through 8-pin EPS may have been damaged vs. power through the 24pin. Seems just really unfortunate timing.