Need PSU replaced, now underpowered

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Well, Dead Island had my rig over the knee...
Not because my rig lacks power but because it lacks power... ok, that was a bit confusing

I strongly suspect my power supply is being drawn too much and that screws up the rest of the system. First game to do that.

Looking for 750W+ powersupply on a budget. Has to have 2x12v rails. Cheap. Wishful thinking ?

At the mo i have quadcore q6600 and 480gtx running 550w OCZ psu (GameXstream?).

Also, 480gtx is rigged with 6pin to 8pin power adapter, since this psu doesn't have any 8pin power connectors (there's hack to run powerful cards, it works but apparently only to the limit.)

At the moment Dead island, if ran on max it is capable of (1920x1080+aa+fineshadows) draws in excess of 480 watts, which is uncomfortably close to rated 550. If i lower resolution and knock off some details, i manage to just about not get rebooting at random times, while drawing about 420 watts...

So, any suggestions as for make and model (and apprx price) of psu are welcome...

P.S. Game is weird, Deus Ex was drawing about 100W less than Dead Island, both being absolutely new games...go figure...

P.S.S. What sort of reserve in wattage should i be thinking about to futureproof my rig ? I plan some overclocking on air. Q6600 SLACR G0 just asks for it, but i cant feed it at the moment, so keeping it stock and safe...

#EDIT1# Case is Antec-900, PSU is mounted on the bottom.

 

[slowpoke]

Only two games managed to reboot my machine without any errors - Deus Ex and Dead Island. I have tried to stoke my rig with other games (Crysis Warhead, Crysis2) none of them tripped my rig to the point of such complete failure.
Temps are good (55-60 cpu Q6600 SLACR stock, up to 80 gpu gtx480 stock), cooling is definitely sufficient, i even reseated and re-greased my cpu, just in case. Didn't help.

550w may be peak output, may not be sustainable for long periods of time.

#Edit1# Any non-game methods to make PSU cr@p itself ? Some sort of burn-in test maybe ? Something that taxes CPU and GPU to the limit at the same time to induce max possible power draw ? For science, so to speak, to prove that PSU is actually faulty/underpowered. I know for certain that major components are fine (CPU/GPU/RAM/MOBO) because all other recent games somewhat held up, but not latest ones... Makes me think PSU any way i twist it...

 

[slowpoke]

Correction is in order: apparently it was 600w GXS. Still, it's most likely faulty.
What led me to this conclusion:
1. Age. I have verified that it was bought in june 2007... ooooold. And runs mostly 24/7. Which cant be good...
2. Today ran loads of tests stressing RAM and CPU, separately and simultaneously. No blackouts. Makes me think, mobo+cpu+ram are good. Prime95 on all 4 cores (most power draw torture) only draws ~300w at the wall (including monitor, which accounts for ~40w). Also CPU temeratures held at 65-67 during the test. Cooling is there and functions.
3. Running ANYTHING graphics intensive reboots PC. And i dont mean Crysis level intensive (old games), but DeusEx/Dead Island/Warhammer40k sort of intensive at 1080p resolutions. Meaning if i drop detail/resolutions considerably the PC will run. Temps are good, GTX480 holds at ~80c. Cooling is functioning as per normal.
4. Running Furmark "no settings" benchmark - almost instant reboot. Well, within 5 seconds of starting anyway.
5. Today cleaned out dust cats out of my PSU and graphics card - no change. Reinstalled new drivers - no change...

Also i must add that most of the power problems started since i replaced my old E6600 to Q6600. Kept stock at all times, knowing that i may not have juice to power the stuff...

Anyway, just ordered OCZ ZX 1000W psu, expect it to rectify my power problems.

@mods and admins: i dug up my old username to these forums, but couldn't change it in my profile at the shop for free delivery for some reason. Anyone care to look into it ? Although i already wasted 9 quid on delivery now (unless of course i can still get a refund... One can dream, right )