Yeah, more heat dissipation could also fit in with what has me scratching my head on the spec comparisons.
You see, starting from the basics, there's a principle in physics refered to as the law of conservation of energy. It basically states that energy can neither be created nor destroyed, but can be changed from one form to another.
There's another assumption which tends to be made that when converting energy to another form, the process of conversion is not 100% efficient (though one can approach greater efficiency), albeit some energy will be lost/unuseable, for instance in the form of heat. Now the PSU, isn't converting electricity to something else, but rather 110/120 Vac into a direct current at the given voltage rails. Hence my wondering with extra draw (550 vs 500 watts being drawn in), what's happening with the extra power...
Now the 5 volt rail is the same, so I won't bother calculating it (given no change). However the cumulative of the 12-volt rails, and the 3.3 volt rail do differ.
OK, pulling up a basic formula here (to relate the differing amperage on the given volt rails, to the actual watts), we get:
http://www.powerstream.com/Amps-Watts.htm
Converting Amps to Watts
The conversion of Amps to Watts is governed by the equation Watts = Amps x Volts
Plugging the respective numbers in, we get:
W(x1) = 28a * 3.3v = 92.4 watts
W(x2) = 25a * 3.3v = 82.5 watts
So, looking at the 3.3v rail, the X2 is using 92.4-82.5= 9.9 fewer watts.
On the 12-volt rail we're using:
W(x1) = 34a * 12v = 408 watts
W(x2) = (17a * 12v) + (18a * 12v) = 420 watts.
This gives us, 420w - 408w = 12 additional watts on the 12 volt rail (which also makes sense when comparing the values to the formula which gives the relation between the values.
For matters of bookkeeping, the additional .5v on the 5vsb should also be computed. There is one thing I don't like with these comparisons however. In relating it back to the power source, one couldn't simply add up the calculated wattages to get back to the source wattage, so there obviously is a problem comparing it over differing voltages in trying to get an apples to apples comparison. The calculated values, in watts,
does match what the box prints up, which when adding up all values on the back, they show up as 608 watts being used, with a source wattage for that end of the PSU printed as 480 watts (the other 20 covering the sb voltage, as well as the -12, -5, and -3.3 rails). The other box I don't have...
If that last variable could be worked out of the results, it could be possible to do such a comparison. We could be seeing extra power draw which essentially heats the room up some more, however...