Do We Need Fancy Multi Rail PSUs For Our PCs?

When choosing a new PSU, it’s easy to get decision paralysis – especially when people sometimes say that multi-rail PSUs are “safer”. They’re also more expensive, and some people say that they can lead to more crashes (in certain cases). So… which is best: single-rail or multi-rail PSUs?

That’s exactly what I explore in this video, where I drill into the history and detail of PSUs to answer that question, and I also show off a crazy expensive PC build that uses a single-rail PSU but might benefit from an upgraded PSU set-up.

If you prefer text over video, please read on for the guide/transcript version of this video.

Video Transcript And Guide

Hey everyone, power supply units are SCARY because they take high voltage mains power from our electric outlets, and then supply this to our computer components. But if we end up with a bad PSU, then our motherboards could be destroyed, our PSU could EXPLODE or the connectors on our RTX 4090s could melt. And I AM exaggerating slightly in this intro – I’ve personally never actually had a power supply unit fail or melt on me, or destroy any of my components. But when you are looking for one to buy, it’s easy to get FOMO and decision paralysis here because there’s loads of different terms out there. Some people say that multi-rail PSUs are safer, other people say to just get a single rail PSU.

Too Much Choice

This is where the Cultists Network website is REALLY useful because it ranks all the different PSUs in tiers – so you know that a “gold tier” power supply is better than one from Jetek… which is in a tier simply marked as “avoid”, which is worrying . But here’s the thing: this PSU list ALSO splits PSUs according to whether they have single or multiple rails, especially at the top tiers.

7 psu list static
The PSU tier list from the Cultists Network

And a quick 1 minute Google search (or ChatGPT session) will SEEM to suggest that multi-rail PSUs are better. And that’s actually where the comparisons to a breaker unit – or consumer unit as we call them in the UK – comes in.

Because effectively you’ve got your big main power supply that comes in, and then an electrician will actually wire everything up into individual bits – individual rails – whatever you want to call it. But if you actually drill into the detail, what you’ll notice is two key things. Firstly each circuit will actually have a different gauge cable. For example my alarm system only has a 1 mm gauge cable, so it’s quite thin and doesn’t carry as much current, but it’s also backed only by 6 amps of overcurrent protection. Whereas if you look at a different circuit – a different rail – for example my cooker, then it has a 6 mm gauge cable which is quite a lot, and it’s backed by a 32 amp overcurrent protection. So effectively that is why the comparison exists between these and multi-rail PSUs, because you’ve got lots of different ‘rails’ with different levels of protection on each of them.

When I first started building computers almost two decades ago, pretty much all PSUs were multi-rail. They had different “lanes” inside of them that would deliver power according to different voltages. You had the 3.3 volt rail for things like the RAM, and then another rail would deliver at 5 volts for things like the hard drives and optical drives so that you could get data from these big shiny round metallic discs without needing to download so much data from the internet. I’m not old, you’re too young! Then you had a “main” higher power (12 volt rail) for things like the CPU and GPU.

Single vs Multi Rail Over The Years

But over the last decade or so, many PSUs actually moved over to be “single rail” (according to half the internet), delivering “everything” on a 12v rail. So the majority of the components would be powered off that single 12 volt rail. And this is where the role of power regulation on the motherboard itself has become MUCH more prominent in recent years, with big chunky VRMs added to the motherboard, to actually help manage the voltage delivery to all the various components. 

However it’s not actually strictly true to say that “everything” runs off 12 volt rails. If you look at your PSU’s manual or look online, you’ll almost certainly see 3.3 and 5 volt entries there.

Corsair website showing the different rails and voltage deliveries
Corsair website showing the different rails and voltage deliveries

And that’s because, even though the ATX 2.0 standard from 2003 actually reduced the power on these two smaller rails, they DO still exist. Your NVMe drives, for example, might be powered from one of these lower-voltage rails. But it’s kinda up to the motherboard nowadays, and it’s not something you need to be overly worried about – unlike “the good old days” where you did need to think a bit more about what rail was powering which components.

So that’s WHY much of the internet, and PSU lists from the Cultists Network, mention “single rail PSUs” because most modern PSUs will power the majority of hardware from the 12v rail. So what does it mean when we say “multi rail PSUs” then?

Multi-Rail PSUs

The beQuiet Pure Power 11 FM multi rail PSU
The beQuiet Pure Power 11 FM multi-rail PSU

Well, a modern ‘multi rail’ PSU like the Pure Power 11 FM actually has two 12v rails. This can introduce some benefits because a “single rail” PSU only offers that single 12v rail, which could potentially be underpowered if you have a super expensive CPU and an RTX 5090 – for example. So technically…

All PSUs are equally multi-rail, but some PSUs are more multi-rail than others…

– misquoting George Orwell.

Having two 12 volt rails is technically better because it allows for more stable voltage delivery than simply chucking everything onto a single 12 volt rail. This means that the internal 12v wires should in theory get less hot in a multi-rail PSU (because there’s less current flowing through them). Also remember when I discussed the breaker unit in a home? Well this has “rail by rail” circuit breakers meaning that if there’s an electrical issue, only one part of the system actually needs to be disabled – turned off. This can help to protect the electrical install in a home, or our PC builds in this context because the two separate 12v rails in a multi-rail PSU will have separate short-circuit and over-current protections built into them.

So that’s great – but what’s not so great is the price of multi-rail PSUs. Even the lower power 850 watt PSU from bequiet is a fair bit more expensive than other single-rail 850w PSUs. And Corsair’s multi-rail, 1500 watt PSU costs a whopping £300 – although admittedly that is a really high power PSU that also supports the latest ATX 3.1 and PCIe 5.1 standards. You’re not JUST getting multi-rail support for that kind of money.

Why You (Probably) DON’T Need A Multi-Rail PSU

But that brings us onto the main question – do we actually need to sell our single-rail PSUs and run out and “upgrade” to multi-rail ones? Aren’t they safer after all? Well Corsair’s website addresses this and makes clear that both types of PSUs are safe, explaining that all their PSUs have the same protective circuitry measures in them to prevent overcurrent and short-circuit issues, for example.

And even if you have a fairly powerful computer, like a 12 core CPU and an RTX 4090 GPU, you should be absolutely fine with a “single rail” PSU – in other words, one that only has a single 12v rail. That’s what most people use nowadays.

Some multi-rail PSUs even actually give you the ability to switch back to single rail 12v delivery, and various people online suggest to do this (if you have ended up with a multi-rail PSU) because some high end GPUs are actually quite demanding from a PSU, and this can potentially cause problems for multi-rail PSUs if their 12v wires deliver lower currents than single-rail PSUs do.

Even This Monster Build Doesn’t Need It

An awesome AI PC build with three RTX 4090 GPUs and a Threadripper CPU
An awesome AI PC build with three RTX 4090 GPUs and a Threadripper CPU

So for CONSUMER systems, even higher end ones, you almost certainly don’t NEED a multi-rail PSU. Heck, there was recently a post on Reddit about someone who made $50k in stocks overnight and built an AI system with THREE RTX 4090s. Totally not jealous.

That had a Threadripper CPU too, and although they HAD power limited the GPUs to just 300 watts each, the entire build was running from a single EVGA PSU which appears to be a single rail PSU.

So if even THAT build doesn’t need a multi-rail PSU, then what does? Well, some of the comments did suggest that the OP goes out and buys a SECOND PSU entirely, and I actually think this would be best – compared to upgrading to a multi-rail PSU in this case. A build like this would still push the limits of two 12v rails, especially if they ended up delivering slightly lower current in a multi-rail setup. That’s not something you really want for an RXT 4090… especially three of them, and also a Threadripper CPU. BUT having two separate PSUs would allow the OP to split up the power delivery in a slightly better way. That’s what I would prefer to do anyway… assuming I made $50k overnight on the stock market. Still not jealous.

The only time I think that a multi-rail PSU really is necessary is when you’re working with very specific niche hardware that specifically says that you need to run it on a separate circuit, or maybe you really think that you NEED the separate over-current and short-circuit protections for some reason. But in all other cases, modern “single rail” PSUs are probably the best bet.

I actually discuss how to connect up PSUs- updated for the latest ATX 3.0 standards – in another video if you wanted to check that out.

cropped A picture of me Tristan
About Tristan Perry

Tristan has been interested in computer hardware and software since he was 10 years old. He has built loads of computers over the years, along with installing, modifying and writing software (he's a backend software developer 'by trade').

Tristan also has an academic background in technology (in Math and Computer Science), so he enjoys drilling into the deeper aspects of technology.

Tristan is also an avid PC gamer, with FFX and Rocket League being his favorite games.

If you have any questions, feedback or suggestions about this article, please leave a comment below. Please note that all comments go into a moderation queue (to prevent blog spam). Your comment will be manually reviewed and approved by Tristan in less than a week. Thanks!

Leave a comment