Which of these 2 is better quality if the price would be equal?

[MSwhip]

1. SeaSonic M12II 520W Bronze Modular spinning on ball bearing

2. XFX 750W PRO750W Core Edition Single Rail ATX 12V 62A 24PIN ATX Power Supply 80PLUS Bronze PSU P1-750S-NLB9

If these 2 were 80 Bronze plus. Does it mean that the real wattages are:
1. 520W x 80% efficiency = real 416 W output?
and
2. 750W x 80% efficiency = real 600 W output?
Is that how outputs work?

It also appears to be that the XFX 750 does not come with modular cabling.
Does that also mean that it is not single rail.
a. What is the relationship between modular cabling and single rail? ... and...
b. What feature i would not get cause of the lack of modular cabling?

I would appreciate the substantiating reasons for whatever opinions you are willing to contribute

Thank you

[Adzsask]

XFX core edition are among the best in there class, and most of the time towards the lower price, used many of them in builds, never ever a problem seasonic makes the core series.

[Bond007]

The wattage on the label is how much power it is able to output, so a 520w power supply can output 520w to your computer (it will draw more than that from the wall if its maxed out).

Modular cabling has nothing to do with rails. In a standard power supply all cables are permanently attached. In a modular power supply some or all of the cables can be detached so you only have to have the cables you need attached to the power supply.

[frontier204]

Originally Posted by MSwhip

If these 2 were 80 Bronze plus. Does it mean that the real wattages are:

Nope you have it backwards and with the wrong numbers... You DIVIDE by the efficiency to get the AC wattage. Also efficiency is dependent on how many watts you are drawing.

A 750W power supply (assuming a good one) will allow your components to draw 750W internally. Same goes for a 520W PSU allowing your components to use 520W. The wattages the efficiency tells you about are how many watts you need to draw out of the wall (for purposes of telling you how much your computer will hurt your power bill). Therefore if you load a power supply to 100%, you will end up drawing more than the number written on the PSU's label.

Check 80+'s web page for the efficiency curves:
Seasonic: http://www.plugloadsolutions.com/psu...20W_Report.pdf
XFX: http://www.plugloadsolutions.com/psu...50W_Report.pdf

For example, 80plus tested that at its 50% load, the Seasonic was 85.69% efficient - see the graph where the "computer" (actually a load tester) was drawing 265.89W, which is equal to 51% of the PSU's rated 520W. To provide said 265.89W, they had to pull 310.30W from the wall. 265.89 / 310.30 = 0.8569 or the 85.69% they read.

Now let's take the 265.89W "computer" and theoretically attach it to the XFX 750W. 265.89W / 750W = 35.45%. Now 80plus doesn't test at 35.45%, so I'l guesstimate with a linear approximation that it's 85.7% efficient (between the 84 and 86% points on the graph where they do test).
So now to get your 265.89W for your "computer", you need 265.89W / 85.70% = 310.26W from your wall outlet.

As for which PSU is better, both are solid units. If you will run your computer 24/7, then you can look at the efficiency curve. Otherwise, just get the one that will run your components as the +10% of efficiency from a bronze to a gold for example will likely not save you money in the long run (e.g. power bill saving will be less than the extra cost of the PSU).

Originally Posted by MSwhip

a. What is the relationship between modular cabling and single rail? ... and...
b. What feature i would not get cause of the lack of modular cabling?

a. There is none!
b. The modular cables
To reinforce my claims, look at the Seasonic M12II and the S12II. They have the same guts inside (assuming Seasonic didn't pull a silent revision) so number of rails, protection, wattage, efficiency, etc. are all the same. The only difference is the S12II runs wires from the PSU's circuit board all the way to the connectors that go to your computer components, while the M12II runs a few of its wires to modular connectors. Note however there is a slight difference in reliability if you don't wire your computer correctly - a modular PSU adds one more point for the connection to fail (between the PSU and the modular cable).
Here's some reading material about 12V "rails" which actually aren't real rails to confuse your further : Everything You Need to Know About Power Supplies | Hardware Secrets

[Dzzope]

get the 750 watt xfx if price is equal (assuming that modular isn't a must for you / fan noise is similar)

[michaelubc]

I would agree with Dzzope.

If both are the same price, The XFX 750W Pro will give you more expandibility for your computer system with a higher wattage power supply; however, if you were comparing Seasonic 750W with XFX 750W, then I would choose the Seasonic hands down.

I have a Seasonic X-1250 1250 Watt and the build quality on that thing is second to none. Seasonic is one of the finest quality Power Supply Companies but it's usually more expensive and there aren't that many sales on these power supplies. They are build to last and have the tightest voltage tolerances.

[Dzzope]

That xfx is a seasonic based unit.. so would be the same apart from casing and cooling (cabling?, modular and connectors provided) as a seasonic unit of similar spec. (and as you said will be cheaper too)