YoAndy :
Because a power supply has a rating of 600w doesn't mean that can be loaded that much.
There is so much complexity that nothing can be generalized. The only thing that can be looked at is one specific unit, and the only way to say something about that one specific unit is based on a professional review of it or one of its siblings based off the same platform. In the Protection Features Evaluation of the
Seasonic Prime Titanium 650W review on Tomshardware, it is loaded to a whopping 925W before overpower protection kicks in, and I quote, "with all of its rails staying within the ATX standard's specifications". Really, the way these companies rate their power supplies depends on a lot of factors. But there is no standard by which rated wattage is derived. For scammer companies they write too high of a number, for companies with a good reputation they write a lower number because then it tests better when tested within those boundaries.
For example, if they had rated that Seasonic Prime Titanium as 750W instead, it would perform slightly less well on ripple and voltage regulation tests (and other stuff, like holdup time tests). So it is in Seasonic's best interests to rate the power supply at a point like 650W where it can do exceptionally on reviews and also have a ton of leeway for large spikes of power, going up to 925W before shutting down.
YoAndy :
In general, a good power supply is between 70% and 80% efficient
That's not true. Look at modern day power supply reviews and you will see this.
YoAndy :
although efficiency depends on how heavily the power supply is loaded
Correct, and 80+ unfortunately is an old standard being replaced by
http://cybenetics.com - fortunately. 80+ only tests efficiency at 4 load levels, so low-load efficiency and crossload situations are never taken into account. Thank goodness for Cybenetics, which is founded by Tomshardware's great PSU reviewer Aris.
YoAndy :
Calculating efficiency is difficult, because PC power supplies are switching power supplies rather than linear power supplies. The easiest way to think about this is to imagine the switching power supply drawing high current for a fraction of the time it is running and no current the remainder of the time. The percentage of the time it draws current is called the power factor, which is typically 70% for a standard PC power supply. In other words, a 350W PC power supply actually requires 500W input 70% of the time and 0W 30% of the time.
Most all modern PSUs have power factor correction, and it's generally 97% and higher all the time. See the
Jonnyguru hot testing of the new Corsair TX850M. Those power factor values are very high. Additionally, the power factor is
not the ratio if output / input power. It is the ratio of active / apparent power. Source: http://www.hardwaresecrets.com/everything-you-need-to-know-about-power-supplies/10/
YoAndy :
Combining power factor with efficiency yields some interesting numbers. The power supply supplies 350W, but the 70% power factor means that it requires 500W 70% of the time. However, the 70% efficiency means that rather than actually drawing 500W, it must draw more, in the ratio 500W/0.7, or about 714W.
You are misunderstanding power factor correction. From
this source on Jonnyguru I get this information: "
Power factor correction won’t make your power supply more efficient (convert more DC output power with less AC input power), but can allow for more devices to be plugged into the same circuit.". A low power factor does not increase input power, that's not how it works. I'll admit I'm not an expert on power factor, it's darn confusing, but I also know what you're saying is not entirely true with all due respect.
YoAndy :
If you examine the specifications plate for a 350W power supply, you may find that in order to supply 350W nominal, which is 350W/110V or about 3.18 amps, it must actually draw up to 714W/110V or about 6.5 amps.
A load table on a power supply does not say anything like this. It merely talks about continuous or peak (hopefully coninuous) power output in amperes on the rails.
YoAndy :
Second, wasted power is converted to heat inside your system.
True. The fan and design of a power supply also plays a role and such.
Lol Calm down your horses. His average system load at the moment is around 500w-550w, if he decides to overclock and run another 1080ti he will be close to a load of 750w. You should know that running a power supply at his maximum capacity is not a good idea. 
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