Okay, I built a computer almost two years ago now and I'm ready to upgrade the video card to an 8800GTS G92. I know very little about power sources, so I need some help picking one.

I currently have a 450W PSU that was built into my Antec Sonata II case (http://www.newegg.com/product/product.aspx?Item=N82E16811129155).

My other components are 2x1GB ram, a 7200RPM hard drive, two DVD-RW drives, an Intel DP965LT mobo, and a Core 2 Duo E6400. I'm thinking I'll get around 650W or higher in case I upgrade in the future. My main question is about PSU fans. My current PSU has the fan on the back, but I've noticed a lot of them have fans on the top, and my case doesn't have an opening above where the power supply goes. Do I have to get another PSU with a back fan? Or are the top fans intake fans? What about PSUs with bottom fans?

Finally, what's a good PSU that works with my case?

Your case will allow you to place the psu however you like, either fan topside or more appropriately downward facing the mobo.

As for the PSU just about any psu will fit your case. I would recomend the 750 watts from either corsair or PC Power and Cooling

So there wouldn't be a problem if I ended up getting a PSU with a top fan and putting it upside-down in my case?

PSU's don't have "top fans". The picture you see of the PSU's with 120mm fans are shown with the psu turned over. The fan is on the BOTTOM of the psu and it DRAWS air into, through, and out the psu's back grill. Also, the psu mounting holes on your case will only allow you to mount the psu with the fan in the "bottom position" anyways, so you can't mess it up. Understand now?

Oh, okay. Thanks a lot.

One more thing: the Corsair 750W or the PC Power and Cooling 750W? Which is quieter? Which is cooler? And what about this one http://www.newegg.com/Product/Prod [...] 6817815002

Is that a good power supply or should I stick with one of the others?

Both are good PSUs, I thing the Corsair might be quieter.

Not the Xigmatec.

Either the PCP&C or the Corsair. I believe the PCP&C to be a fraction better but obviously depends on budget etc.

Your present power supply is sufficient for that card:

425W PCI Express-compliant system power supply with a combined 12V current rating of 28A or more
One 6Pin PCI Express supplementary power connector

I agree, your current PSU is powerful enough to run a single GTS 512 so just buy the card and when your ready to upgrade you can buy a new PSU.

Check this out http://www.newegg.com/Product/Prod [...] 6814134037

A 450W Antec PSU is plenty for any single-GPU setup (save for GTX280). I would use it until (or if) you start having problems.

Avoid the Xigmatek.

Another good PSU would be the Thermaltake Toughpower 750wt. Having used both the PC P&C and the TT Toughpower, I can say that the Toughpower is a lot quieter. For reviews on good (and bad) PSUs, go to http://www.jonnyguru.com/index.php . Also, I doubt need a 750wt PSU. Use a PSU calculator such as:

http://www.extreme.outervision.com [...] orlite.jsp

That calculator WAY over compensates on certain components.

This is a much better resource:
http://www.atomicmpc.com.au/forums [...] t=9354&p=0

That shows the actual power consumption of each kind of GPU setup, add your CPU TDP and 10-15W per HDD or ODD, 20-30W for the motherboard and you have a good estimation of power usage. Ideally, your system should run 50-70% load (of the PSU) with all components fully loaded (for efficiency purposes). Power supplies acheive maximum efficiency between 40-55% rated load.

Edit: BTW, you can run an 8800 GTX with an Antec Earthwatts 380 PSU (just to give you an idea of what is 'needed' rather than what a calculator says) -
http://www.overclockers.com/articles1452/

How are OCZ power supplies?

Everything you need to know:
http://www.xtremesystems.org/forum [...] p?t=108088

Personally, I think there are better choices out there that are cheaper and higher quality than OCZ units.