It should be noted the average efficiency of any given PSU really depends on the average load it will be under.
If you hover over the Bronze and Gold logos seen here
, you will see those 85% and 90% efficiency ratings occur when the supplies are running at 50% load.
This means to achieve maximum efficiency, you need to properly size your PSU based on the average demands your computer will put on it.
Most people would would be surprised if they saw how little power their computer consumes if they put a kill-o-watt meter
in line, or monitored power consumption through a UPS. While I am just typing in this webpage while streaming music via Pandora, this modestly pushed i5 with 16GB of RAM, 2 SSDs, and a R7 graphics card, my computer is pulling just 108W from my UPS and note that includes my wireless router, modem and two
24" LED LCD monitors which are powered from the UPS too.
My point is, if you had a large Bronze, it could be supporting a small 20% load at 82% (or less) efficiency most of the time (less if the load was less than 20%). But if you had a properly sized Gold and the load was 50%, it would be working at 90% efficiency most of the time.
Not sure I understand the math used above.
If your computer requires 300W, it will pull from the PSU 300W. It does not matter if the PSU is a 450W PSU or a 1000W PSU, good efficiency or lousy. It will pull 300W.
And regardless the size of the PSU, the PSU will pull from the wall, 300W plus 30 to 45 more to make up for inefficiencies (assuming 85 to 90% efficiency). So the cost difference (assuming 10 cents per kWh) is closer to $2.00 ($3.50 with 82% and 90%) - admittedly not much no matter how you look at it. But of course, the differences would be greater if you average more than 4 hours per day.
But there is more to it than just efficiency. Where does that wasted energy go? It goes out the back of the PSU in the form of heat. If your PSU is running hotter, that could signal the fan to spin faster to keep the PSU properly cooled. That means more fan noise. If your room is air conditioned, your AC needs to work harder. True, still talking pennies, but they add up.
Also, as a general rule, it costs more to manufacture more efficient power supplies. It takes a better design and more efficient components. It is just a common practice in virtually all industries to increase quality and features in the higher lines. Cadillac vs Chevrolet, Lexus vs Toyota, high end Sony TVs vs entry level Sonys. I am not saying they are more reliable or will last longer, I am just saying as a general rule, they perform better.
While not a steadfast rule, as you move up the line of 80 PLUS certified PSUs, you end up with a supply with better ripple suppression and regulation too. This equates to a more stable output - something your computer components will enjoy. For all these reasons, I have no problems justifying the higher costs of a Gold supply over a Bronze.
I like to say you wouldn't buy a brand new Porsche then fill it up with generic fuel at the corner Tobacco and Bait Hut.
After all, if you spread the extra cost of a better PSU over the life of the PSU, that amounts to pennies too. But there's a good chance, with your computer components receiving cleaner power, and your PSU running cooler, they will last longer as well.