I need a PSU and I need one fast!

Hi-
Here is my situation. I am building a computer, and right now only have the case. After I hooked up the fans (1x 120mm, 1x 80mm, 1x 140mm), the computer wouldn't start. All the fans would make about 1/4 revolution, and that is IT. I know that it is the PSU because it's only a $20 400w supply. I am going to need a new one anyway, due to the new components that I am looking at, but I wasn't expecting it to be this soon. The current estimated wattage is 313w, but with 2-way SLI it comes to 513. Will a Corsair CX Series Modular CX600M be enough to have 2 GPU's later on? Or should I get the 750w one? Again, I need to get just the supply this week, and the other components will come sometime after Christmas.
 
I would avoid the CX series

Sizewise ....find ya card here....

http://www.geforce.com/hardware/desktop-gpus

Click on it and then select "Specifications" on left

Scroll down and add the "Minimum System Power Requirement " (covers system + one GFX card) and "Maximum Graphics Card Power" (covers 2nd card) together for system requirement on non overclocked system

Example

http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-650ti-boost/specifications

Thermal and Power Specs:
97 C - Maximum GPU Temperature (in C)
134 W - Maximum Graphics Card Power (W)
450 W - Minimum System Power Requirement (W)4
One 6-pin - Supplementary Power Connectors

Stock system....Corsair TX, XFX Core Edition, Seasonic M12 .... Overclocked system - Corsair HX / AX, Seasonic X
 


In the post above yours I used a 650 Ti Boost as an example... you can use that site for all cards

Thermal and Power Specs:
97 C - Maximum GPU Temperature (in C)
134 W - Maximum Graphics Card Power (W)
450 W - Minimum System Power Requirement (W)4
One 6-pin - Supplementary Power Connectors

450 watts for system w/ 1st card + 134 for the 2nd so according to nVidia ya need 584 watts minimum

So that would be a 650 if not overclocking anything, a 750 if ya are.

Thermal and Power Specs:
98 CMaximum GPU Temperature (in C)
230 WGraphics Card Power (W)
600 WMinimum Recommended System Power (W)
One 8-pin and one 6-pinSupplementary Power Connectors


If it's a 770.....

http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-770/specifications

Thermal and Power Specs:
98 C - Maximum GPU Temperature (in C)
230 W - Graphics Card Power (W)
600 W - Minimum Recommended System Power (W)
One 8-pin and one 6-pin - Supplementary Power Connectors

600 + 230 = 830 minimum .... bigger if overclocking

As for the modular thing.....modular provides no advantage and some disadvantages. No sense in making a cable modular if it absolutely must be used. All it does is add another failure point an extra resistance / cost.

Most quality PSUs are what's called semi-modular. All the cables that absolutely must be used are hard wired....all the optional ones are modular.