So it's a 1000W PSU, and all the rails added up equates to 1800W. Obviously that's not anywhere near the 1000W of the PSU. Does this mean that each rail can support up to a maximum of the rail wattage, but the overall PSU can't support all the rails? Seems weird it would be set-up like that, almost a bit misleading
Important thing to understand about rails, they do not provide power, they merely limit the power you can draw from the unit along a certain grouping of wires to keep you from overloading a set of wires or connectors.
All of the wires on a rail run to a single OCP(over current protection) chip which will shut down the unit if you try to draw more than a certain amount of power from it, however it does not generate power, it merely decides if it should cut off the power coming through, all of the rails then join back to a common source which takes the AC power from the wall and converters it to 12V DC(in modern units even the 5V and 3.3V rails are derived from the 12V source), this source is not meant to feed all of the rails at the same time.
The OCP on a good unit is set higher than it should be if you were to add all the rails together, this means you dont have exact power per rail, you wont be unable to use 50W because it was allocated to rail one only, in a well laid out unit it would be able to be used by rail two or rail one because of how the OCP is set.
99% of the time, you cannot just add all the rails together to find the combined power, generally if you look through the pictures of a unit on newegg there is a picture of the load table sticker on the side of the unit, this should list a combined rating for the 12V rails, either directly under their portion or in words below the table, if it doesnt its impossible to know the total combined power available between the rails, but its highly unlikely its the sum of the rails.
Yeah I think thats the conclussion that I came to, in my weirdly worded post, it just seems like the rails are set really high in comparison to the overall wattage. I bought the XION PSU when I was just starting with tinkering with my computer, and now in hindsight I wish I had bought a better brand with maybe 1 beefy 12V rail, maybe 2.
single rail or multi rail doesn matter,those limits on the cables are the point at which they can individually handle the load yeah your rails might be together rated higher but your psu can only provide its set amount between them