Vegan

check the SATA cables, lots of times they do not last long in my experience

Seems my H115i RGB fans are running at 500 rpm suggesting something is amiss.

Cables on Corsair's site are less costly

I have accumulated power cables from all over the planet. My RM650 was a Chinese model so I swapped out that cable for a NA variant and powered it it up. Modern power supplies are 90-240V automatic unlike the ancient models which a switch.

I use MSI motherboards and their BIOS has all kinds of options for the CPU fan as well as the fan headers. The MB fan headers are not in use so I have them disabled which is the default. The CPU fan is enabled but the alarm is not. The Alarm can be set to one of several temperatures. I can post screenshots of my BIOS if you need clarification or you can find the manual for the MSI X470 Gaming Plus or MSI X570-A PRO on the MSI support pages.

I am using iCue 4 for my H115i which is still working. Firmware is not usually needed. The older H100i is starting to get close to the end of the road for service life. AIO water coolers tend to last maybe 5 years or so

My Corsair cable box has lots of single PCIe cables and pigtail PCIe cables. I have many power pig cards and I found the single cable and pigtail combination works with cards want three PCIe cable connections. Try a R9 Fury card which needs over 300W of power to run it. The RX 480 was actually slightly more powerful while using less power.

the power output suggests the fan is switching on and off and may be slow to get rolling

Of the very few I know with cream puff rigs and vertical graphics cards had a pile of custom hardware and cabling to go along with it. My Obsidian 750D is a large but conventional EATX box with lots of room for the H115i water cooler. On the front was an option for a 420mm radiator but I elected to install a third cage and stuff the machine with lots of hard disks. Even with 3 cages there is still room for 11-12" video cards but the RTX 2080 I have is a measly 10.5" long and it's easily installed. The RTX 3080 is longer and thicker. It fits too. I have a R9 Fury so I can test fit giant power pigs.

I use Intel based laptops and they have been stable. I use AMD desktops because AMD offered PCIe 4.0 2 years ahead of Intel.

Corsair still lists obsolete models for users who may have questions about a particular model. AFAIK high power rated power supplies are in short supply due to digital coin mining.

The image of an ITX chassis clearly shows nowhere to place the huge triple slot RTX 3080 while the suggested 275R is dramatically more spacious.

I own an FLIR camera and my H115i RGB is very close to ambient I have seen a lot of garbage readings suggesting software is defective and hardware sensors are not standardized

Update your BIOS, AMD fixed that and several other bugs with this years ROMs

I would go for an AX1200 just to be sure there is abundant power

RTX 3080 and SFF do not mesh well A pint sized card like my EVGA GTX 1060 however would fit like a glove

Now you know I use 1000W+ power supplies I have long used power pig video cards so I can speak from experience, never cut corners with the PSU

The RTX 3080 is a tad big for ITX formfactor mashups. A more conventional box like the Corsair 275R can squeeze in the RTX 3080 and the SF750 is enough to handle the card

could be the usb cable is damaged As long as the box is running fine it's a minor nuisance make sure the LED is green is all you need

AM4 machines do not enable the CPU fan fail alarm unless intentionally set. The CPU has a thermal throttle so it saves itself from harm if the cooler fails.

Before my AX860i died I used a single rail mode and it never was a problem. Now I have an HX1000i also in single rail mode and it also is not a problem. Even dual cards are not an issue.

I do not use the MSI software for RGB as I use a Commander Pro myself. My H115i also has a fan controller. So I have more than enough fan headers for my larger chassis. 2 front fans, one rear and two on the water cooler is all I have. Corsair has a box for adding more RGB if the commander comes up short.

That is rather unusual to see the USB fry like that. Makes me think there is a short circuit somewhere in the unit.

check for a BIOS update as that might improve stability

cable extensions are risky for high power loads