150A = 1008w
This is the total output that the power supply is capable of. Don't worry.
25A + 25A + 25A + 25A + 25A + 25A = 150A
Watts = Amps * Volts
On the 12V rails it lists 1008W as the max power, so 1008W divided by 12V is only 84A, thats still quite a bit of power. 6 rails at a max of 25A each does NOT mean that you can add them all up and get 150A off the 12V source for the unit. The rails do not provide power, they just watch and shut down the unit if more than a certain amount tries to flow past them, they all draw from a common source which is almost never capable of feeding them all entirely at the same time.
150A @ 12V would be 1800W of DC power, in north america your household wiring provides 110V nominal to a normal outlet, to get 1800W from an outlet you would need to pull more than 16A from the wall, your average household circuit is only 15A so it would trip every time you loaded it up, there should have been multiple this doesnt make sense moments.
@OP the power requirements for the cards are for the system as a whole, and the PCI-E connectors would be on different 12V rails, as long as you arent using adapters you dont have to worry about the rail limits, they already designed around that, you just need to look at the total power available for the unit's 12V rails which in this case is 1008W(84A)
Single rail or multi rail really doesnt matter these days so ignore that and only look at the combined power.(ill explain why it doesnt matter farther down)
The PSU has 84A available, a GTX 580 uses about 280W which is about 23A, so two of them would pull about 46-48A, which leaves about 30A(360W) available for the rest of the system which is more than enough, the next most powerful item in the system is the CPU which needs less than 150W(~12A), everything else in the system needs minimal power so that unit has more than enough power for 2 GTX 580s in SLI running at full power with some overclocking.
Now for the reason why the rail splitting doesnt matter.
There are a few customary ways to do it, what i am guessing by their distribution of connectors is that they opted for this.
The CPU gets its own 12V rail for the 8 and 4+4 pin connectors(this used to be mandated in an OLD ATX spec but has long since been dropped but some companies still do it)
One rail feeds the motherboards 24 Pin main connector and some drives, another rail feeds the rest of the molex and sata power connectors
Since there are 6 6+2 pin PCI-E connectors there are likely 2 per rail, this works out pretty perfectly for their rail distribution as an 8 pi PCI-E connector is rated for 150W(12.5A) so two per rail gives you 25A, the max capacity of the rail, now, this is fine as any card that bears the PCI-E logo(the 6990 and the ASUS ARES do NOT bear the logo as they exceed the rules) is not allowed to draw more than 300W of power, it gets 75W from the slot and 225W from the PCI-E pin connectors allowing at least 75W of extra power available to OC with.
The site you linked to doesnt have any better option for high powered units like 850W units, so as long as the price is reasonable i would go for it.
and one last thing.. would the 1050w be safe..?
( no melting wires? or something under heavy load.. )
- been reading reviews / people talking about single rail and multiple.. etc..
and it made me confuse more..
at the site..
there are some 1000w psu..
this CoolerMaster GX-750 750w 80PLUS for 1/2 price of cougar 1050
Thermaltake GRAND 80+ GOLD 750w same price w/ cougar 1050..
FSP Everest 800w 80PLUS modular for 1/2 price of cougar 1050
Thermaltake LitePower 700w 1/4 price of cougar 1050
men.. the deeper i get, the more confuse on which PSU should i take..
The Cougar has more power than any of those, and units like the GX 750 certainly shouldnt be used(has major issues with ripple over 60% load) the lite power is a bit lite on power, the FSP everest is an older model, it got discontinued on newegg already so its not high on my list, it was a decent unit but not spectactular, the Thermaltake Grand 750W is a good unit but if its the same price as the cougar i would go for the cougar.