In this setup I can play games at highest settings at 720p and at 1080p some details off(due to the damn CPU).
the seasonic 12V supply had dual faces: 12V1 and 12V2. My mobo just has single input of 12V. So I made the chassis with single 12V1 supply and hell the whole system is working. the 2nd one just kept aside.
My question is simple, is my mobo all the power from the single 12V1??
i mean all the 365W?? or just 185W.
and still if 185W the max load from the power supply calulator is 250W.
The power supply uses current limiters to prevent too much power from being taken on a single "rail". They both get all the power they need from a larger single rail.
Each rail on an ECO-400 has a limit of 17 amps(per google) or 204 watts. now as long as both rails together do not pass about 360 watts no problems will happen. Clearly this means you can not load each rail up to 204, but one at 204 and the other at 150 would be OK(not that you want to run the power supply that hard).
The rail distribution is not up to you. the power supply may put all drives and the motherboard on one and just video cards on the other while another may have video and cpu share with all other devices on the other(normally the yellow wires on the power supply will have a stripe(different colors of 3+rail units) and solid color to show the rails).
So you are NOT limiting your self by using a 4 pin instead of an 8 pin cpu power on your board or a 20 pin vs 24 pin ATX connector. If that is all the board has, that is all the board was made for.
In reality the "rails" are just to prevent a user from pulling too much power from the wires on the power supply. This is the same as how your house lets say has a 100amp service and then each breaker set at 10 amps to prevent you from exposing the household wires to more current than they can take.
You have 360W of power available from the 12V rail, you have all of this available. The CPU connector will be on one rail while the motherboard and pci-E connector will be on the other, this helps to spread the load out so you don't over load any single rail. The manufacturer already figured out how to lay out the connectors so that you won't have too much load on any single rail.