PSU or UPS Problem? HELP!

I dont understand one thing.. when i check by throwing the breaker down (which as the experts say that it simulates a power outage to check the UPS) nothing happens and the PC keeps on running during game where the GPU+CPU+PSU is on full load and stress. I even checked the GPU load with the help of GPU-Z and tested several games on it like Assassin's Creed: Brotherhood uses GPU 40% to 60%, Bulletstorm as well, Super Street Fighter IV uses on 25% to 30% GPU Load and PC dont restart on them. However Crysis and Metro 2033 especially uses almost 100% GPU in some places and it's average load on GPU is 90% and above. So lets say Playing games like Crysis and Metro 2033 which are Hardware hungary apps uses the Maximum power off the system in easy words the PSU is at it's Peak Load.. but i remember exactly the day i installed this new Graphics Card AMD 6850 i ran Crysis 2 times and played it until the Power-Failure happened and PC did'nt restarted.

Also i do remember when i installed Assassin's Creed: Brotherhood my other applications started to give me errors. Yahoo Messenger gave me error and some other application was crashed so i updated my Windows and those errors and crashes were gone and fixed but later after several days when i ran Crysis and power outage happened this problem started.

So is there a possiblity the Windows has something to do with it after updating it? Does throwing breaker down from the DP really simulate an actual Power-Outage or it has to be a proper real power failure/outage from the Grid. What is this Mystery?

By pulling the plug for the UPS from the wall is fine to simulate a power outage.

My UPS is a SVC-1200VA it's a chinese made but well made unit and it's quiet popular here. It has AVR and <10ms of transfer time and other features etc. APC are very expensive here and i'll have to pay 3 times the price of SVC for 1 1200VA APC unit

@ kool1zero
You could be right and it's happening something like you mentioned but idk how to check problem and it only happens when power goes off by the grid and only when my system is running some game which uses GPU @ full load.. never restarted by pulling the plug out and throwing the breaker down i checked more than 10 times randomly in past 2 days... is there anyway to check it and fix it?

Bilal, what do you have connected to your UPS? I have my PC, Cable modem, router, and monitor on the back up outlets. I have a 750VA APC BackUPS unit set to shut down after 5 minutes of power outage.
For pure PC protection you don't need to have speakers, printer, or scanner on back up. You would do well to get a APC, Tripp-Lite, or CyberPower unit.

First of all sorry for late replying coz i just sent my motherboard in warranty as it has voltage sensor problem and got new one as replqcement :) but i did'nt assemble my pc yet. Also bought new PSU Cooler Master GX550w 80Plus Brone today in order to provide better and clean power to PC :)

@Britton30
I'm only using LCD, PC and Wireless Router which are plugged in a Power-Strip which is connected with the UPS in 1 Power Outlet although the UPS has 3 Outlets but im using one due to Power Socket that is 7 feet away from Computer not using anything else.

@kool1zero
I'll try with it too but i did not understood little what to do about Surge Protector

I hope that too :) thanks for all the Help kool1zero, Britton30, TBoyd and Zepher :) I will let you know the results when i will test again idk but still my heart beat start pumping fast when i think if something will go wrong again .....