Introduction

It has been 16 months since our last power supply review, but the long wait is finally over. We have a new PSU and cases editor, and this is the first of many new PSU reviews to come. The first PSU to hit our new testing lab is the S12G 650W from Seasonic. Seasonic is a company that hardly requires any introduction; they are one of the oldest and most reputable computer PSU designers, manufacturers and retailers. Today, their products are held in very high regard by experts and enthusiasts. The company has their own retail range but they also serve as an ODM for many other well-known brands.

The target groups of the S12G series are advanced users, enthusiasts, and generally those who are not afraid to pay a bit more for advanced performance. It has impressive specifications and features, including an 80 Plus Gold efficiency certification and a "Smart and Silent Fan Control", as well as a five-year manufacturer's warranty. Despite that, it does not really break the bank, as the 650W version that we will be testing today retails for $89.99 plus shipping, a price that appears quite reasonable for such a product.

A year or two ago, you would have had a hard time trying to find a high quality 80 Plus Gold certified unit for that kind of price; however, today Seasonic's retail range has tight competition from several other manufacturers, such as Antec, EVGA, Rosewill, and others. As the Seasonic S12G is not a modular unit and doesn't really include any special features, the company clearly relies on quality and performance above all else; middling quality and average performance cannot be tolerated when several other manufacturers are breathing down your neck. Let us see if the 650W version of the S12G can live up to Seasonic's reputation.

Packaging and Bundle

Seasonic supplies the S12G PSU inside a fairly well designed cardboard box, with a black/blue color theme. The front of the box is tidy, with just a few badges with the certifications of the unit on display. The sides and rear of the box however are littered with information about the unit, in several languages.

Companies rarely supply anything noteworthy alongside their PSUs, especially the non-modular models, but the Seasonic S12G appears to be an exception. Besides the usual power cord, manual, and screws, Seasonic also includes a few cable ties, three blue/black velco cable straps, and a case badge with the company's logo.

External Appearance

The Seasonic S12G sports a small, typical ATX-sized (140mm) chassis that has been sprayed with a matte black paint. Some effort has been made to improve the appearance of the power supply, albeit not all of the measures can be considered successful. Seasonic uses all-black ribbon cables, with the exception of the 24-pin ATX cable that uses typical color-coded wires and sleeving. A blue sticker has been placed on the rear of the unit, where it will be visible from the back of a case once the PSU has been installed. Oddly enough however, the company sprayed the series logo in white on the right side of the chassis, where it will be facing the right side panel of a case. It goes without saying that it will not be visible inside the vast majority of the cases currently in the market. On the other hand, the sticker with the specifications of the PSU has been placed on the left side of the chassis. No effort has been made at all to enhance the top side of the chassis visually, so in a bottom-mounted location users with case windows will simply see a black surface.

Internal Design

We were surprised the instant that we opened up the chassis of the S12G 650W unit. The unit is cooled by an ADDA AD1212MB-A70GL fan, unlike the majority of Seasonic's other models that use SanAce fans. The particular fan model is high quality, featuring a "Hypro" liquid bearing and with a maximum speed of 2050 RPM, yet it is no SanAce. When you have to compete in the mainstream market and even a few dollars can make an immense difference on sales, you have to keep the retail price as low as possible, which is most probably why Seasonic went with the ADDA fan for the S12G. Note also that as this unit has no fanless mode, it does not require a fan with extraordinary specifications (e.g. a very low starting voltage).

It is obvious that the OEM behind the S12G is Seasonic, as the company designs, manufactures, and markets their own units. We spot four heatsinks; the smallest one handles the rectifier bridge, the one near the edge of the PCB cools the active PFC components, and those on each side of the main transformer handle the inversion and conversion transistors of the primary and secondary stage respectively. The input filter begins on the PCB attached to the back of the receptacle, but continues on the main PCB until the input of the rectifier bridge. We spot a total of six Y capacitors, two X capacitors, and two filtering inductors, which form an excellent intake filter.

In terms of component and build quality, Seasonic does not let us down. The primary capacitor and most of the smaller capacitors are supplied by Nippon Chemi-Con, with some Rubycon electrolytic capacitors after the secondary side heatsink as well. Everything is well shielded and secured with glue, ensuring the mechanical cohesion of the unit. The inductors are glued and also tightened with cable ties, in order to minimize the chance of vibration-generated noise (also known as "coil whine"). The quality of the soldering is very good, well above what we would consider average. There are a few spots where excessive solder has been applied, but that hardly is worth commenting on in a $90 MSRP PSU.

Test Equipment and Methodology

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700W, a Rigol DS5042M 40MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox, and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs - 2014 Pipeline post.

Cold Test Results

At room temperature, the Seasonic S12G 650W unit easily honors its 80 Plus Gold certification, reaching up to 94.4% efficiency at 50% load. Inside the normal operating range of the power supply, which is between 20% and 100% load, the efficiency remains above 90% at all times. In fact, if the S12G was just a little more efficient while heavily stressed, it could hit 80 Plus Platinum status.

As expected, the efficiency drops sharply when the load is below 20% (130W in this case), dropping down to 76% with a 32W load, but it goes up to 84% when the load is increased to 65W. These are considered "out of range" conditions and do not affect the 80 Plus certification of the unit, but considering many modern PCs will idle at 40-60W, it's still worthwhile to look at performance at these loads. Of course, at 32W load the difference between 75% and 85% efficiency only amounts to around 5W at the outlet.

Both the air and the heatsink temperatures might appear a little high for a unit of this capacity and efficiency operating at room temperature, but that is because the fan of the Seasonic S12G 650W PSU is being "lazy" -- or "quiet" if you prefer. The fan is thermally controlled and it looks like Seasonic decided it didn't need to spin faster under such testing conditions. During our SPL testing, the fan reaches audible levels only after the unit hits ~80% of its rated output.

Hot Test Results

From the table below, it can be seen that the output power quality of the Seasonic S12G is very high. The maximum voltage ripple that our instrumentation recorded is a mere third of the ATX design guide suggested limit (the limits are 120 mV on the 12V line, 50 mV on the minor voltage lines), under full load and inside the hotbox no less. Cross-load testing negatively affects the power quality of any power supply but its effect on the Seasonic S12G is small, with the 12V line registering up to 54 mV while delivering 512W. Cross-load testing has virtually no effect on the minor voltage lines, the performance of which did not degrade any further than during standard testing.

The impact that the higher ambient temperature has on the energy conversion efficiency is rather small, reducing the efficiency of the Seasonic S12G by about 0.5% across the entire load range. As such, the Seasonic S12G easily retains its 80 Plus Gold efficiency certification status even inside a very hot environment. The average efficiency between 20% and 100% load is an extremely high 91.6%.

The difference between our cold and hot tests is an increase of over 20°C ambient and, naturally, all of the temperature readings increase significantly. We dare say that the temperatures of the heatsinks rise quite a bit beyond our expectations of an 80 Plus Gold unit by Seasonic; however, the heatsinks are rather small and the design of the power supply apparently focuses on low-noise operation, so sacrifices are made in the area of temperatures.

The low-noise aptitude of the Seasonic S12G becomes apparent when we see that the fan hardly exceeds 38 dB(A) under the harshest of conditions, which is an audible figure but hardly louder than three or four 3.5" mechanical disks -- and never mind the GPUs that would be required to hit such loads. Nevertheless, unless you somehow manage to maintain the unit at maximum load inside a >50 °C environment, the Seasonic S12G will not get nearly hot enough to cause problems.

Final Words and Conclusion

Today we witnessed the reason why Seasonic is so popular amongst enthusiasts and advanced users. The 650W version of the S12G is not the cheapest of its range and class, it has no extravagant features, and it is not even modular. When you look at it, it is yet another all-black ATX PSU; not even the ribbon-like black cables are in any way special nowadays. You can easily find an 80 Plus Gold certified and modular 650W PSU for around the same price.

On the other hand, when it comes to build and power quality, the Seasonic S12G can easily make most of its competition shudder. Seasonic usually picks very high quality components for their units and the S12G is no exception, with most of the primary components and all of the capacitors coming from Japanese brands -- and the S12G is their mainstream series, not their high-end brand! That alone says a lot about Seasonic's commitment to quality and why they so easily cover a mainstream unit with a five-year warranty.

Looking at the performance charts and tables, the Seasonic S12G could probably be offering the best all-around performance within its price range. The DC output power quality is excellent and the voltage ripple suppression is remarkable. Since voltage ripple is directly correlated with the longevity of electronic equipment, especially capacitors (it causes self-heating), very low ripple readings benefit the durability of your system's components. The energy conversion efficiency is very high and it maintains its high efficiency and quiet operation even inside a very warm environment.

Its Achilles' heel is that the S12G tends to run a little hot if heavily loaded for prolonged periods of time while inside a very warm environment; however, the only real-world scenario that we can imagine that would replicate such conditions is that of a powerful cryptocoin mining system built inside a poorly designed chassis. If you are planning to use the Seasonic S12G for powering such a system in a $20 case, that probably is a bad idea. However, if you are looking to buy a PSU for its high quality and performance and consider aesthetics and modularity to be secondary or unnecessary features, the Seasonic S12G is definitely worthy of strong consideration.