Single Rail vs Multi-Rail Power Supplies
When building a PC one of the main components you should never cheap out on is your power supply unit. This crucial component delivers current to your entire build therefore you should always try to invest in the best possible option for your budget.
A big talking point related to PSUs in the past was whether the unit you are interested in is single rail or multi-rail. With modern PSUs, this is nothing you should be bothered about and instead, you should focus on other specs that will determine if the power supply you are interested in is a good fit for your build.
Single Rail vs Multi-Rail
As explained in this handy video a simple way of understanding the single rail vs multi-rail debate is to think about it in terms of safety. A single rail means that the 12V that the PSU pulls from the wall is running through a single circuit.
A multi-rail PSU on the other hand will have multiple 12V rails (pathways if you will) for different connectors. For example, each PCIe connector that goes to your GPU has a separate rail/trace, your CPU power cable has a trace, your 24-pin motherboard has a separate rail, etc.
The fact that the load is distributed along multiple rails makes it safer and is understandably preferable since it can identify a localized issue and shut down the PSU faster. At the same time in modern times, multiple rails can also be replaced by a single 12V rail but that is split into multiple pieces because it measures current in different spots allowing the PSU to shut off earlier in case of too much current being sent preventing burned components.
Single Rail vs Multi-Rail Does Not Matter
The fact of the matter when it comes to multi vs single-rail PSUs is that this spec does not matter at all currently. Modern PSUs are often either single and multi-rail at the same time as Corsair PSUs, or are marketed as single rail while being multi-rail and vice-versa.
The even bigger reason to not bother with the whole rail discussion and look at other more important specs (power efficiency, modularity, wattage, etc) is that even a single 12V rail PSU that was engineered right is capable of powering your machine as long as it is designed well and has the load distribution done correctly.
Modern power supplies all come with a bunch of safety features and long warranties so as long as your PSU has enough wattage for your build you can safely overclock your components (CPU/GPU) and do intensive tasks with no issues.
Purchasing a reputable power supply from a reputable brand with enough wattage and a bit of overhead is all you need to do nowadays. What a great time to be a PC gamer.