https://thinkcomputers.org/settling-the-debate-multi-rail-vs-single-rail-power-supplies/ 
 
Rails.. What are they, exactly?
Part of the venom towards multi-rail PSU’s stems from a completely incorrect assessment of what multi-rail actually means. Multi-rail PSU’s DO NOT use any more power sources than their single-rail counterparts. In fact, almost all PSU’s, with the exception of some extremely high wattage units, only use one.

 
It all comes down to a little thing that protects your system from overvoltage and potential computer bonfires: OCP. OCP is Over Current Protection. OCP will monitor your +12v power source output for current surges, spikes or simply too much current that could end up causing damage to your components. There is OCP present on the other PSU rails too, but we’re not talking about those.
So what is a single-rail power supply? Put simply, the entirety of the +12v power source is monitored on a single circuit, monitored by an OCP chip configured to shut off if the power supply’s max Amperage is reached.
In contrast, a multi-rail PSU has multiple (2+) monitoring channels on the +12v power source, each with a separate Amperage rating which is a division of the PSU’s maximum rated output (plus perhaps some additional headroom to prevent shutdowns from reaching the top-end) . Some rails are dedicated to different things, so you’ll have higher-rated monitoring channels for PCI-E connections and CPU power, along with lower-rated ones for hard drives and such.
So there you have it. Is the power cleaner on either? No. They’re the same power source. Does it affect ripple or electrical noise? Not really, at least, not significantly enough for it to matter to .. anyone.
Which is better?
The answer, simply, is neither. They’re effectively the same in the way they deliver power to your components.
There is however a benefit that one of them offers over the other: safety. For low wattage units this doesn’t matter, as the max Amperage will be triggered on either single-rail or multi-rail PSUs in the event of an overload. However, as you reach higher wattage units, you’ll find that it’s very difficult to hit the max Amperage of the PSU on a single-rail unit. Chances are in the event of an overload on the +12V power source, it’s going to potentially burn your components or itself before OCP kicks in. In this scenario, multi-rail PSU’s are better simply because each rail has a lower Amperage rating that is a portion of the power supply’s maximum. It’ll make the OCP easier to trigger, and therefore, more likely to save your components from harm.
But when considering a power supply to purchase with efficiency, clean power delivery, ripple, noise, etc.. the answer is, pick either, because the results will be the same.
 

Dyezak
Looks like Over Current Protection is handled differently via multi or single rail.  

Thanks for the details.
Maybe this multi-rail over current protection has some compatibility issues with the GPU's which demand a lot of power or the Corsair AX-i -series powers have some design flaws..

Been having the same problem with my 3090 FTW3 ultra with a Corsair HX1000i, just switched it into signle rail mode so fingers crossed get the same issue with the HX series

Corsair RM850x single rail.  No issues with 3090 FTW Ultra.

Soppa
I have experienced a lot weird display driver crashes since changed to 3090 from 1080Ti.
I tried a lot of different settings and crash happened mostly out of the games, while playing videos in desktop VLC/browser.

I tracked the problem to Corsair AX860i power which was set into MULTI-RAIL config from corsar link software.
When changed power to SINGLE RAIL, all crashed had gone! At least so far :P

Maybe the problem is when GPU is running on low MHz/voltages and suddenly wants more power and this causes some sort of issues when Multi-Rail is set on.
I don't know what multi-rail is but if its some kind of protection system, maybe there is big enough latency before psu gives power out and this causes the issues?
Anyway, this seems to fix my problems with the GPU.
Cheers,
Soppa

Multi rail shares the overall electricity of your PSU to multiple rails that have an allocated maximum wattage per rail they can hold. So technically you have a big rail with more wattage and then the rest with less wattage handling things. Going single rail is the best for the average user me thinks I mean with a reputable PSU you don't run into danger of overpower overcurrent etc they all have safety measures and you can use an overcurrent plug at your wall anyway like an APC etc.
 
Glad this worked for you.

So far its worked perfectly since the change, did not want to reply too soon but gone from having 2-3 crashes a day to being fine

Thanks to the OP for this advice.
 
I thought my 2 week old 3080 FTW3 Ultra was on its way out like others. Got black screens when playing games or on a render workload and instantly thought of the posts on this forum about issues. I checked the cables were OK and in good shape and installed corsair iCUE for my AX1600i PSU. It was on Multi-rail, switched it Single and hey presto, gaming and rendering is working again.
 
Fingers crossed it stays this way. My 3080 is a 2012 SN edition with Black lips.

matthew.moles
Think I may have replied a bit too soon, in the three days since my last post, I have had 3 driver crashes :(

Did you check that it has not turned back to multi-rail after computer shutdown or so?

So it was still set to single rail, but Icue had been misbehaving a bit. I restarted and its been fine since so seems to be good, though think would look out for one with a physical switch next time

cochrane484
I'm having the same driver issues and want to try this fix. I have a evga supernova 850w P2. Any clue how to switch it to single rail?

There is an actual physical switch on the PSUs that have multi and single rail. Very similar to the OC/silent bios switch. If your PSU supports it there should be a relevant switch.
 
Edit: As far as I can see, your PSU is single rail.
 

Soppa
I have experienced a lot weird display driver crashes since changed to 3090 from 1080Ti.
I tried a lot of different settings and crash happened mostly out of the games, while playing videos in desktop VLC/browser.

I tracked the problem to Corsair AX860i power which was set into MULTI-RAIL config from corsar link software.
When changed power to SINGLE RAIL, all crashed had gone! At least so far :P

Maybe the problem is when GPU is running on low MHz/voltages and suddenly wants more power and this causes some sort of issues when Multi-Rail is set on.
I don't know what multi-rail is but if its some kind of protection system, maybe there is big enough latency before psu gives power out and this causes the issues?
Anyway, this seems to fix my problems with the GPU.
Cheers,
Soppa

I created a custom fan profile in the Corsair Link software for my HX750i which now runs at a minimum of around 900 rpm. I found that in games the 3090 FTW3 Ultra gets my PSU sort of hot. At least hotter than I have ever seen it before installing this graphics card. Without the new profile the fan was not switching on soon enough or fast enough in my opinion. Now the fan on the PSU also helps with the overall case air flow. 

Wow, I was considering it now I am second guessing tho, well see what happens