In The Box:
(1) M12II power supply
(1) Bag of modular cables
(1) Power cable
(1) User's Manual
(4) Installation screws
(1) Case badge

 
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Specs:

Features:
Externally, the M12II looks nearly identical to the S12II with the exception of the modular cable design. Because of the modular cables, the casing is a mere 20mm deeper on the M12II. The only cables that are hardwired on the power supply are the ATX 20/24 pin strand, one 4-pin 12V and one 8-pin 12V; the rest of the cables are entirely modular (and all sleeved). All the connections on both M12II models are outlined in the chart below. I must point out that I've always liked the way Seasonic handles the floppy drive connectors. Instead of putting them on a couple of the Molex cable strands, just to get in the way for those who don't use them, they've actually put them on a separate adapter that you can plug into one molex plug and get two floppy drive power connectors.

 
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On the inside, the only major enhancement the M12II brings to the table is a slightly enhanced +12V rail system. The 12V rails have been upped slightly and now provide 420W of output power instead of only 408W in the S12II. I was disappointed to see the lack of solid state capacitors in the M12II. Having solid state capacitors has many pros which were well discussed in the S12II review, and for those looking for the absolute best power supply for their money, that can be a huge selling feature. If Seasonic were to pack solid state capacitors into a modular power supply like the M12II they could really have a beast on their hands. The caps used under the hood of the M12II seem to be all Japanese made which aren't too bad (generally preferred over Chinese made capacitors).

In terms of energy efficiency, the M12II shares the same 80Plus logo as the S12II did. Seasonic claims these units can reach up to 85% efficiency! What does this mean for you? Not only an extremely quiet power supply because it will run cooler, but since your energy is being used more efficiently you could also save slightly on electricity bills if your system is on a lot.