Settling the Debate: Multi Rail Vs. Single Rail Power Supplies

Ever since multi-rail PSUs were introduced, we’ve seen enthusiasts adamantly claim that one or the other PSU type is better. Some claim single rail is better for overclocking. Some claim multi-rail is safer. Single rail is cleaner. Multi-rail more efficient. The list goes on and on, so who’s right? People on either side argue their points and pick up uninformed followers along the way, resulting in the same rehashed marketing over and over again from companies playing on this vehement fanboyism: A single strong 12v rail! Multi-rail for extra stability! Blah blah. Which is better? How does this apply to me?

Keep reading, and I may just give you an answer.

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.

The next time you read something like this, feel free to ignore it, laugh at it, or get irritated at the fact they’re playing on people’s’ lack of understanding in order to push their products:

“A single +12V rail provides stability, ease of use and the ability to deliver clean currents under a heavy load.”

It seems a very large proportion of power supply manufacturers are doing this, when they don’t need to be.

We hope this helps clear up any misconceptions people may be throwing your way with regards to power supplies, and helps to better inform you when making your next purchasing decision.