Seasonic M12II-620 Power Supply Review

Seasonic is back with an old favorite aiming to make it better for the end user by giving you now Bronze level 80 Plus certification. Our tests are more harsh than 80 Plus' tests, so let's see how exactly Seasonic's new M12II 620 watt PSU takes to our more stringent testing conditions.



Today's Seasonic M12II-620Bronze is the 4th Seasonic branded Seasonic power supply we have seen to date, but by far not just the 4th Seasonic unit overall . To date all of the Seasonic, and Seasonic OEM, power supplies we have seen have been quality units that were something users could easily buy with confidence. However, winning streaks have a tendency to eventually end. Is today the day that Seasonic's string snaps? Or does their new revision of an old platform in the M12II-620BRonze have the legs to soldier on another day as a good value/mainstream option for users on a budget? Let's see.

HardOCP’s testing methodology is intended to very much push power supplies to their advertised wattage rating in temperatures that will represent some of the hottest computer enthusiast cases. So if a unit passes all our testing it is definitely not something to take lightly. In fact we expect more power supplies to fail our testing than make it through unscathed.

Build Quality

The exterior of the M12II-620Bronze unit is trimmed out in typical Seasonic fashion with a high quality fit and finish. We once more find the standard retail production finish to be a tough black not quite flat but slightly textured finish paired with well sleeved cables. Once we move to the interior of the unit and we look at the construction in context of what the design is, an older double forward group regulated design, we find the interior integration/construction to be clean and well done. The components are well seated, the soldering is generally well done even on the modular PCB, and it looks tidy (minus the sometimes liberal use of caulk for securing components). Further, the component selection for the unit is generally very good with the capacitors being a mix of Nippon Chemi-con (primary and most of the secondary) and Rubycon (secondary) capacitors so we can't complain about this selection at all. So while not a modern design, we at least see that Seasonic still uses quality components and does a good quality job building their not quite top of the line units. However, we do find the quality control to be a bit missing in a couple of other aspects. Namely the manual and warranty information. The manual includes a few details about the unit found on the box, some installation instructions (those four screws are tricky), and the power label for the M12II-500. Oh this is the M12II-620Bronze we are looking at, right. Ok, well, at least it includes the warranty information for the M12II, no wait it doesn't do that either. Ok, well, at least the warranty information is on the box then. Ah hah, now we have it. The warranty for this unit is listed as being 5 years, or 3 years. It just depends on which side of the box you look at. The Seasonic website lists the warranty as being 5 years so with 2/3 of the warranty information saying 5 years we are going to go with that being the actual length.

Load Testing

The Seasonic M12II-620Bronze passed our normal load tests at 45C even though it is rated at only 40C. During that process everything seemed to be doing well with only one point of real note and that is the 12v voltage regulation which was a bit looser than what we have seen from some other Seasonic offerings. However, its drop of 0.33v over the unit's 48A capacity does fall in line with what we have seen from similar types of group regulated designs such as the BFG MX 680W. The minor rails, which were much more lightly loaded, held to much tighter voltage regulation which is good to see. The efficiency was also good overall, meeting its 80Plus Bronze advertisement for all intents and purposes, as it ranged from 83.87% to 84.93% at 120v and 81.60% to 83.56% at 100v. The exhaust temperatures during the load tests were a bit warmer than what we have seen from previous Seasonic units, but given the high quality capacitors and other components used these peak values of 66C and 68C seem manageable.

Moving on to the transient load tests we find the M12II-620Bronze to be once more posting a pass but with some noteworthy results. When directly loaded the 12v rail saw a peak drop of ~400mV in Test #2 and ~390mV in Test #1. The 5v rail when directly loaded saw a peak drop of ~160mV in Test #2 that was coupled with a drop of ~120mV when the load on the 12v rail was being triggered. These results are rather large in magnitude and seemingly a bit out of place as the smaller in capacity, yet similar designed, S12II-500 did better than this unit in these tests. Why the M12II-620Bronze did worse is unknown, but it did stay in specification so the unit passes this set of tests as well (though this aspect of the unit could use some work).

DC Output Quality

Overall the DC Output Quality of the Seasonic M12II-620Bronze is excellent across the board. The 12v rail peaked at just ~25mV of ripple/noise while the 5v rail was below ~10mV of ripple/noise throughout testing and the 3.3v rail came in at a bit less than 20mV. The 5v rail was even better behaved as it never really even managed to peak above ~10mV of ripple/noise. These values are very similar to some of the results we have seen from Seasonic, Corsair, and BFG that have floored us in the past. As such, today the DC Output Quality of the Seasonic M12II-620Bronze is one of its best selling points.


In the course of our reviews Seasonic has consistently produced some of the quietest power supplies we have tested (notable other examples being from Enermax and BFG), with the exception of the PC Power & Cooling Silencer 750 which was downright loud, even in our ~53dBA testing environment. Today, however, we are looking at a lower powered (620W) Seasonic unit under their own brand and to date the single quietest power supply we have reviewed (the X-750) was produced under Seasonic's own brand so we had great hopes that the M12II-620Bronze would follow more in its footsteps. These hopes were largely realized as the M12II-620Bronze stuck to Seasonic's roots of being almost dead silent. In general, the M12II-620Bronze easily matches all other Seasonic units, save for the X-750, that we have seen to date in its perceived noise output. There was no time during our load testing or working with the unit that it became audible in our test environment. As such, with the M12II-620Bronze Seasonic continues to produce products that are certainly appropriate for quiet cooling environments.

Paul's Thoughts:

The Seasonic M12II-620Bronze is a power supply that is kind of hard to quantify in some ways. It is very much an older design and its load tests bear that fact out. However, at the same time it is still well built and performs excellently in other aspects such as DC Output Quality and noise output. When reviewing this unit it seemed to fit well as a replacement option for the no longer available BFG MX 680W as it had all of the same highs and lows as that unit but with better efficiency and a lower a price tag. That price tag is also what is going to be one of the driving factors on this unit as with it, this fits the exact same market segment that the MX 680W used to and this is a segment where there is not a lot of good options available currently at reasonable prices. So users who previously looked at, or were considering something like, the MX 680W (a midrange ~600W power supply that has excellent DC Output Quality, good build quality, is quiet, is efficient, and modular) really should be considering the M12II-620Bronze. And those users who did not consider that unit at the time but are looking for something that fits that bill today should as well. It is not a perfect product, but at the price point there isn't much that beats it out there in general availability today that we see.

The Bottom Line

The Seasonic M12II-620Bronze is a new midrange power supply from Seasonic that has most all of the characteristics we have come to expect from Seasonic. The unit features a large single overhead fan that is quiet, has good efficiency values, a semi-modular design, and enough power and connectors to run the majority of systems that users will be building. In addition to these design aspects the M12II-620Bronze also has very good DC Output Quality and is very well built. On the downside, the older group regulated design shows some weaker 12v regulation and transient load response. However, with a current price of $89.99 it is hard to find very many other units on the market currently that can continuously outperform the M12II-620Bronze at the same price point. The M12II-620Bronze is a solid value. As such, while not a premium unit the M12II-620Bronze is definitely a very capable entry to midrange unit that would do a good job for most builds including single-GPU Fermi systems.

Seasonic is giving away FIVE of these brand new PSUs in our forum. Hit this thread to enter.

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Seasonic M12II-620Bronze