I guess the Corsair model has been designed by Seasonic itself.. There are differences though.. The 650TX is non-modular and hence lesser costing as compared to the X-650 which is fully modular and more costly.. The advantage of a modular design is with better cable management.. The X-650 bears a 80+ gold certification also making it more efficient than the 650TX.. My recommendation would be something like the XFX 750W Black Edition or the Corsair HX 750.. It all depends on your budget and rig configuration.. What are your PC specs BTW.?
Did not see that Corsair was not modular, thanks. My first build, GA-P55A-UD3, I7-860, GV-R577SO-1GD, G.Skill 4GB (2 x 2GB) DDR3 1600 F3-12800CL9D-4GBNQ, Western Digital Caviar Black 1TB 7200 RPM, Nzxt Hades and SeaSonic X650. Modular power supply a must for Nzxt Hades case. Despite Seasonic reputation it appears I have a DOA.
There are a lot of differences between them. Keep in mind that the X-650 is the best that Seasonic can do, whereas the TX-650 is a mid-range PSU.
The X-650 is one of the best PSUs you can find on the market. Its highlights are the silence (the fan only works if nedeed), modularity and efficiency. Needless to say, the rest of the features are very good too. However there is many others options that are cheaper and performs very well too (Corsair HX650, Antec TruePower New 650W, XFX XXX Edition 650W, Thermaltake ThoughPower XT 675W, Cooler Master Silent Pro M 600W, Enermax Modu82+ 625W, ...)
The TX650 performs very well and it's much cheaper, however, it presents only two PCIe conmectors, is not modular and the ripple/noise is a bit high. Anyway, It's a quality unit too.
You can find some useful information and reviews about these and other PSUs in the RealHardTechX's PSU Review Database: http://www.realhardtechx.com/index_archivos/Page541.htm
Ripple and noise on the 12 volt rail(s) are really not that important. The two main consumers of 12 volt power (CPU and GPU) are going to convert it down to a much lower voltage. By then, ripple and noise will be filtered out. And drive motors don't really care either.
I have the Seasonic X-650 Gold in my current pc. I purchased the psu about 8 months ago when it was first introduced. I can confirm that it is a silent psu. During normal everyday use and typical gaming the fan does not come on. Instead, the psu is cooled passively. It's a unique design that works well. The modular cables are a little longer than typical psu's. I have the Lancool Dragonlord K-60 case. I did not need an extension cable to reach the 8 pin power connection at the top of my motherboard. Every once in a while I use a utility to measure line voltages. So far they have been well within acceptable limits and rock steady.
I also have a Corsair 620 watt modular power supply. I think I bought it 4 or 5 years ago when it was first introduced. I used it almost everyday until I built the new pc about 8 months ago. I never had any problems with the Corsair unit. It is now in a spare parts box in case of emergency.
The use of modular power supplies is a personal matter of preference. I use modular power supplies to help with cable management. The modular units come in handy in smaller cases where there isn't much room to hide cables.