New power supply

So I've decided to upgrade my computer a little bit and I am switching my 4670 for either a 4850 or 5750.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814102824
or
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102865

The only problem is that when i built my budget computer I did not realize just how important the power supply was and bought a 460w Cooler Master which from what I have read is not very good to say the least lol. I am not sure if it will run either so I want to be safe side and buy a new one. I will not need a very good power supply, just one more reliable and better quality, as I will only need this computer for a year or two playing games such as wow or source games at 1600x900 resolution. By then I will have joined the Air Force and will not have as much time to play games. I have read that corsair is good so I am considering this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139003

I will probably get the 4850 as I do not use dx11 and because of the cheaper price. I want to make sure that this power supply will suffice.

Current Specs:
7750 BE 2.7
4gb Ram
HIS 4670

Corsair is the best PSU you can buy. I have built 7 or 8 pcs with them inside. I have had 2 for almost 2 years and they still run whisper quiet and come with one of longest warranties for a PSU. They are built very well and even the packaging its in is good quality.

Personally I would go with a 550 for a little more money. Corsair being the quality it is you can get by with the 450 and be ok but 500-550 is the sweet spot for any pc that doesnt have multi drive arrays in it, dual video cards and a bunch of other shit. Two things you should never skimp on are your motherboard and your power supply.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004


And far as the video card, I wouldnt waste the money going to a 4850 from a 4670, the difference would be marginal at best really.

Since you listed a 144 card as a possibility I propose you this one for 149.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814129146

Visiontek makes a damn good product, the last 5 video cards Ive had in my game pc were from them and never had a issue. I even called their customer service once asking about the step up program they have an a actual english speaking guy answered and knew what the hell he was talking about, that was aces in my book. But they have real lifetime warranties on their cards and have a track record for being nofrills cards which is why they are reasonably priced always and for reliability.

I think for the low cost upgrade, the OP's original proposal of 4850 512MB + Corsair 450W (~$160) seems like a fairly good route to take. 4850 is actually quite a step up from 4670, especially when the details are turned high and some AA turned on. This article shows some good comparison among cards, importantly so between the 4670 and the 4850. 5750 performs nearly the same as 4850, so I don't see the price being 45 to 50% more to be justifiable. The Corsair 450W is good enough for the 4850, and Corsair is a good brand indeed. But now Newegg has the Antec 550W for $55 after $10 rebate with free shipping, so that's a good $30 saving over the Corsair 550W and same price as the Corsair 450W. Antec also makes good and reliable power supply, so if you can get on this deal now, I would do it.

I think i may go with the 450w one considering that this may be the only upgrade i do for this computer. Another question tho..how do single rails go vs dual rails this has always confused me as I know you do not just add the amps together.

Corsair, Antec, and PC Power & Cooling are nice for PSUs. Although PC Power & Cooling are coming out with some new products, so Newegg doesn't have much of a selection up there right now.