Replacing old PSU - new GPU GTX 750 Ti w/ACX Cooling

7 year old system (specs below). Recently returned a bad HD so also returned my old 8800 GTS, which was leaving behind bits of pull down menus even though it functioned in games. EVGA replaced with GTX 750 Ti w/ATX Cooling.

Received both pieces the same day so installed and began the tedious task of updating 7+ years of Vista updates. I generally leave my PC on so was on for 24 hours (about half that idle time). The next night I shut it down. The next morning, after the BIOS and before the welcome, the PC lost power. Gone.

After a couple of weeks of trying to isolate the problem, I discovered it was 2 things - a dead GPU 6pin and a dead sound card. Both had worked prior to this. I pulled out the sound card and plugged in my other 6(+2) connection from the PSU and everything works. But now I'm afraid to turn it on again!

First the specs:
Mobo Gigabyte GA-P35-DS3L BIOS F7 (2008 or 2009)
CPU Intel Core2 Quad Q6700
Zerotherm CPU Fan
2x2G Crucial Ballistix
1T Seagate Barracuda 7200
DVD Burner
DVD Player
Hauppauge TV Tuner
USB Keyboard & Mouse
8 spot USB Hub
3 case fans

Current PSU: PC P&C 610W Silencer

I've contacted Gigabyte & EVGA regarding this issue and get it's (new GPU) incompatible/it should work but nothing definitive. The old mobo of course isn't UEFI, which I'm told is okay as long as it POSTs. But, if I understand it correctly, that is actually when it went wrong earlier. The gist is that I'm not 100% that it's the PSU but am thinking of replacing it just to play it safe and then hope the GPU isn't responsible!

I can't afford to replace the parts right now because I'd have to replace nearly everything, including the OS. I've already invested about $40 from the expense of shipping my defective parts under warranty, so looking for a PSU - not top end and not garbage - that will hopefully work. At some point in the future I'll update to something like the i5-4590, new Mobo and 2x4G RAM but my calculations show the new products shouldn't need any more wattage because of efficiency. The new GPU usage is much lower than the old 8800. I'm thinking 550W. Would 500W work with these specs as well as anticipated update?

The real issue, other than cost, is my case. I have the Antec P182SE case - full sized with the power at the bottom and the CPU connection at the top. I had to install the PC P&C upside down. So I need a PSU with a long CPU connection. Additionally, the new PSUs have the fan on top, which means if I have to turn it upside down, I'll have to get a modular because my unused cables are stored under the PSU unit.

I had a thread going at Tom's but I got taken out of the discussion when a war over the quality of Corsair was heatedly debated and I hadn't even suggested Corsair! I don't mind someone telling me a PSU isn't good if they tell me why and if the discussion still includes me and my needs. :)

I was looking at Antec (thought since my case was Antec the cables would fit) but have added Corsair (Newegg has some good deals/rebates right now), Cooler Master and whatever else similar. Thoughts? Suggestions? THX!

Replacing old PSU - new GPU GTX 750 Ti w/ACX Cooling