Windows 7: How to Pick the Right Power Supply

The wattage rating of the PSU has nothing to do with watts drawn from the wall plug.



A PSU that is 90% efficient will deliver 90 watts to the PC when it draws 100 watts from the wall.

A PSU that is 83% efficient will deliver 83 watts to the PC when it draws 100 watts from the wall. If your components require 90 watts, that PSU will have to draw 109 watts from the wall to deliver the 90 watts.

109 x .83 = 90.47.

That's the advantage of efficiency. In the above case, the 90% efficient PSU pulls 9 fewer watts from the wall than the 83% efficient PSU, and yet both deliver 90 usable watts to the components.

The more efficient PSU saves 1 KWH per 111 hours of operation. 9 watts x 111 hours is about 1000 (1 KWH).

So--if you were paying 38 cents per KWH, you'd save about 57 cents a week if the thing were running 24/7, with the more efficient PSU.

That's for a PC requiring 90 watts. Double that for a PC using 180 watts. It would be over a dollar a week.

I wouldn't save anywhere near that much as I don't pay 38 cents and don't run 24/7.

Sorry mate I did a typo I should have said that because the output is rated at 450 watts doesn't mean the primary circuit ie the mians transformer is drawing the same from the mains supply I have built a fair few in my time and yep I looked a right royal chump eh?

Oops I should have added too that a total wattage "crossover" is impossible to because of the loss in heat dissipation via the wirings and components as physics will tell you so viza vie 100 watts at the wall is hardly likely to reach even say 95 watts at the output of the secondary circuit.

Maybe this will help. It's an excellent article from one of my comrades at TH.
Power Supply Efficiency Myths - Power-Supplies-PC-Cases-Case-Mods - CPU-Components

Note the "dishonest" vs. the "honest" efficiency graphs.

In real world, if my poor aged Mum needs to know how much does I do cost Her per year, Me better be 90% efficient honest the day she'll ask me the bill. I wouldn't notice Her tricks.

Should i've bought a 80+ Platinum?

Yes! For the reason the bill will be less to pay and the bullet in my head will not go as faster and i will be able to keep my stuff before running to hell, anyway!

Lesson is learned!

The bottom line...

After a week reading Psu Ratings and Specs, calculating what max watts under low/full load i should need for my system & components to run smooth and not being overkill in the choice of a too high voltage rated PSU.

I arrived to decide and choosed a full oem semi-modular 700w 80+ Gold (87,5%-93%) efficiency under 20% to 50% load. Is a Dual-GPU ready certified Psu list for my graphics & with c6 support, ErP 6 Ready.
Which was also better rated and efficient than a value one 650w 80+ Platinum.

Backed up my cheapest GX 650w v2 in the cupboard. It'll serve me only in case not being stuck!

Why 700w instead of 750w?
The reason is quite simple.
-I'm not planning upgrading in a few years my mains components and i surely will add some peripherals but they will not change too much in the PSU power consumption.
-The Psu will be efficient & economic for my bill only if i can use it at the right load, so i far prefer lower watts and better efficient states under loads.
-700watts (58A) is far what i need and i'll not reach the peak load more than a second, anyway!!
-The Psu is enough branded to.

This was just not an easy task!

Yep Non I still cannot make up my mind between the Corsair HX 650 52A (624 watts) or go $50 more for the HX 750 62A (744 watts). Both are gold rated and like your choice semi modular.

My Sandy Bridge runs a HX 650 (bronze) and to be honest doesn't even raise a sweat!

As you might have noticed i choosed in between!!! Semi-modular was convenient, i can cut also discuss for full modular and full railed 12v.

Some also said to think how much Amp the motherboard takes & how much Amps the graphics takes.

Yeah Non on looking I found my usual supplier reducing a Corsair HX 1050 80 Plus Silver by $100 which is only $30 more than the HX 650 so I think I would be mad not to get that eh?

Some says that PSU watts doesn't matter as it could load less fan spinning and heat. Looks it is up to you, now.

That's the counter part...Silver but higher watts or Gold and less watts....Is the question!?

Yes I suppose you are right I honestly hadn't thought of the heat issue and besides the 650 is a gold and is going to be able to be made to look tidier eh?