500w and gtx 680?????

get a better PSU and you will have a much better margin for safety not to mention a longer service life

http://www.hardcore-games.tk/wp/psu.php

For a system using a single GeForce GTX 680 graphics card NVIDIA specifies a minimum of a 550 Watt or greater power supply that has a combined +12 Volt continuous current rating of 38 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important factor.

Overclocking of the CPU and/or GPU(s) will require an additional increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock you are trying to achieve.

When I overclocked my rig the power consumption rocketed up.

Simply...any 500W PSU will be sufficient...if you plan to SLI Later you'll need a 700W PSU.

So you would claim that a Cooler Master eXtreme Power Plus 500 W Power Supply is sufficient?

Did I specify Cooler Master Extreme Plus by name?

Since the GTX 680 draws max 220W according to techpowerup test & review of the GPU, So any quality branded 500W PSU with 2 x 6 Pin PCIE connectors should be very sufficient for the OP's system.

And since you mentioned a name, so the Antec Earthwatts 500W would be my choice.

The word any certainly includes the Cooler Master eXtreme Power Plus 500 W.

OK. So I edited my post above, Any Quality Branded PSU  

the power supply ocz 500w modxtreme pro has a 18amps on the dual +12 volt rails so 18x2= 36

ok so i found a psu which has 550w and two +12v rails with total amps on the +12v rails of 38amps

Get the one I mentioned above, OCZ ModXtream and StealthXtream had some quality issues.

yes but i have to stick to my really tight budget. my budget is £720   and a zotac 680 and a 2500k itselfs cost about £500!!!! and what about the other parts!!
i am thinking to get
corsair 400r
gigabyte g1 gurrila used on ebay
ocz zs 550w
8gb pkr 1333mhz ram
zotac geforce gtx 680
my used samsung 2.5 inch hdd
and liteon 24x optical drive
i will not be buying on newegg since im in uk

sorry not a 2500k a i7 920

OCZ ZS is great according to the review of jonnyguru, and it will be sufficient for your needs.

At first you said FX 8120, then i5 2500K, now you say i7 920.
?????  

i changed the build  

^or just trolling?from fx to SB to 920?
i smell fish