Take each part and google it with TDP. for example, TDP of 6870 is 150 watts, TDP of your processor is 125 watts, chipset etc. is another 50. Total of well less than 456w on 12v.
So it all works and the PSU is barely warmed up because components don't all take peak draw at the same time.. So if you measure your system at the wall with a 'kill-a-watt' meter you see numbers like 300 watts total system. 300w at 80% efficiency = 240 total draw actually going to the parts well less than PSU max.
Now overclock the snot out of it. With high voltage, high frequency and high temps. Current leaking through the chips insulator all over the place. Your video now pulls almost 250 watts, processor is up to 200 and things get interesting for the 456w +12v, but the 456w still has enough amps to handle it. http://www.tomshardware.com/reviews/processor-power-man...
Before this thread is done you will probably have a dozen people posting in here about how much it sucks, just warning you ahead of time.
With PSUs, brand is everything. There are only 4 brands that everyone here will agree are worth spending money on. Those are:
The reason that people will agree on those is because the first 2 are made 100% by Seasonic and the last 2 are Seasonic made like 50% of the time.
Personally, I wouldn't buy the last 2 because of that 50% of the time they aren't.
If you haven't got this PSU already, I would highly suggest you don't get it.
If you do have it, I would highly suggest you start saving for something good like an XFX 550w.
Believe it or not, the XFX 550w can put out about 2x of what the Ultra 650 can at room temperature.
It has to do with testing standards, I think. Like how there aren't any. One model could be tested in a furnace and the other in a freezer and the resulting wattage slapped on the label.
Temperature greatly affects what PSUs can output, so a PSU tested in a freezer won't put out anywhere near stated wattage at room temperature.
Most people that try to cheap out on the PSU also have top mount PSU cases (in my experience) which compounds the problem because the heat from in the computer has to go into the PSU and effectively stay in there (amount out = amount in).
If you had a bottom mount PSU case, you might get away with it, but your first order of business either way should be to save up for a better PSU.
Antec and Corsair have different levels of quality. That's where the difference is. My TruePower is as good as anything on the market in it's efficiency range. You just have to pay attention to specs and read some reviews to be able to choose good stuff.
What is the point in going through the effort to read reviews if a perfectly good alternative exists?
I don't see any good reason not to just avoid the reviews entirely and buy XFX. They cover the whole range, hitting every 100w between 450w and 850w which powers the energy needs of like 99.9% of all PCs.
It saves you many hours of research in the process.