Help with power issues

[Whotek]

I just got new hardware to update my old PC. I'm not a professional in this, but I can manage myself xD
Is practically a new PC. I kept the Power Supply, DVD drive, Case and HDD.

My PC is randomly turning off and restarting, I'm almost 100% sure the problem is power and I completely forgot about this when I ordered the new hardware :/
The GTX 680 SC needs a minimum recommended power supply with +12 Volt current rating of 38 Amps and my PSU is 20 Amps.
I have a few questions, can the low apms cause my PC to randomly turn off? Is there a temporary fix while a new PSU arrive?

Thanks in advance for the help!

PC information bellow:
Asus P8Z77-V LX
Intel Core i5-2500K Processor
EVGA GeForce GTX 680 SC Signature
XLR8 8GB (2x4GB) DDR3 1600 (PC3-12800) CAS 9 Dual Channel Memory Kit
Old Power Supply:
BFG GS Series GS-650 Power Supply

[Valiea]

I feel like that PSU is a few years old. Personally, I would just scrap it and buy a new one, because it looks like, and sounds like, your PSU is the problem. Hey, I might be completely wrong, but the last thing I would ever do is skimp out on a PSU when I'm going for a brand new build. Basically because I've heard too many horror stories about bad PSU's frying GPUs and MoBos and CPU's and all other kinds of nonsense.

[kidsafe]

Your PSU basically has its wattage split in half, so 240W on one 12V 'rail' and another 240W on another. Since a GTX 680 is capable of using around 225-250W or so under GPU Boost, you're basically running into overcurrent protection and your PSU is shutting itself down. If your 6-pin PEG connectors are labeled, try using one from the 12V1 rail and the other from the 12V2 rail.

[Emberhelm]

Kidsafe nailed it....if that doesn't work, buy a new PSU, preferably one with 80+ Bronze cert.

[Whotek]

Your PSU basically has its wattage split in half, so 240W on one 12V 'rail' and another 240W on another. Since a GTX 680 is capable of using around 225-250W or so under GPU Boost, you're basically running into overcurrent protection and your PSU is shutting itself down. If your 6-pin PEG connectors are labeled, try using one from the 12V1 rail and the other from the 12V2 rail.

Thanks a lot for the information
In the mean time I underclocked my GPU so it would not peak and cause the PSU to shut-down.

My PEG where not label and I only have 1x6-pin and 1x6+2pin PEG connector.
Now, I think, I understand how this 2 rails system works. Sadly I couldn't find which cable are in which rail :/ While I don't have another PEG connector to work with I used the 2x4-pin to 6-pin PEG adapter, I used a cable line of 4-pin connectors that I never use to do this.
I really don't know if this solves the issue since I don't know If the video card is receiving 40amps now or still taking 20amps from one rail. Is there is a way to monitor the amperage in a piece of hardware?

---------- Post added 2012-05-02 at 08:03 PM ----------

Update:
After more testing the problem still here :/ I underclocked the GPU again while I wait for a new PSU.
I bought Rosewill Green Series RG630-S12 630W
This PSU has +12v@50 amps I need and the 80+ certification Emberhelm recommended.
Thank you all for the help