I checked out the computer you bought--looks pretty nice! I also totally support your decision to get a new PSU. I would get a new PSU even if you weren't upgrading your video card. I can tell from the pictures that that is a "Power Man" or something along those lines, which is a cheap generic power supply that we used at a place I used to work. Not JUNK, but junky.
For $70 you can get a decent PSU. Corsair is a really good brand. Now about the CX series: I've got a CX430 right now that works great with no power issues. However, it has a real annoying whine that, while it doesn't effect operation, just shouldn't be there. This seems to be a common issue on at least some of the CX models.
If you are set on a CX, it looks like you could get a CX600M on Newegg for the same price as a nonmodular one (it's on sale, may as well.) I would, however, recommend taking a look at Corsair's TX series. They also look like they are on sale (looks like you could get a 750W for the same price as the CX600 after rebate, and Corsair is good and fast with rebates). The TX series are generally built better and have a longer warranty (5 years vs 3 years.)
Seasonic, Sparkle, FSP are also really good ones, though they are pricey! I myself just missed a ridiculous deal on a Sparkle that I keep kicking myself for...an 80+ GOLD certified 650W for $60!
As far as the video card goes, maybe someone else can help you out! But read reviews on the PSU!
--Technic58--Joined 07/25/2004--Post Count + 13,953--
Desktop: AMD A8-6500 Richland, Asrock FM2A88X, 8GB Team DDR2133, WD 500GB Black, XFX HD7870 and Sapphire HD5870 (mining), EVGA NEX650G PSU, CoolerMaster HAF 912
Laptop: Acer Aspire TimelineX 3820TG: i5 460M 2.53GHz, 8GB DDR3, 640GB Western Digital HDD, ATI Radeon HD5650M, Windows