Seasonic G Series 550W PSU - Introduction

When it comes to high performance computer power supply units, Seasonic is one of the most reputable manufacturers. The company serves as the OEM of many other well-known brands, such as Corsair and NZXT, but they also have their own retail branch. A couple of month ago, we reviewed one of their most advanced and powerful products, the Platinum 1000W; an exceptional power supply by all means, which however is meant for hardcore enthusiasts and highly demanding professional users alone.

Seasonic G-550 550W Power Supply

Today we will be taking a look at another highly advanced product from Seasonic, yet one meant for the bulk of advanced users and gamers, the G-series 550W power supply. As the series name suggests, the G-series products come with an 80Plus Gold certification. The current pricing of the specific model we are going to examine $89.99 shipped. For an 80Plus Gold certified and modular 550W power supply, this is not a bad deal at all nowadays. Will however the G-series 550W power supply perform anywhere near as well as the monstrous Platinum 1000W did? We will find out in this review.

 Seasonic G 550W main capacitor

Seasonic G-550 features and specifications


Unboxing the Seasonic G-series 550W

The box

We received the G-series 550W power supply inside a glossy white box of average size. Seasonic's artistic themes usually are very serious and this product is no exception, with only a graphical abstract of the letter "G" formed at the front side of the box.

The box (rear)

Seasonic is using the entire rear of the box to display the features of the power supply. Specifications and other details can be found on the sides of the box.

Bundled items

Despite this being a power supply of average output, the bundle is rather rich and surely better than we expected. Seasonic supplies a case sticker and mounting screws, several black cable ties, three high quality branded cable straps, the A/C power cable and a well-written manual.

The cables

Seasonic supplies the modular cables of the G-Series 550W power supply inside a reusable black pouch. Seasonic is using all-black flat cables, even on the PCI-E connectors.

External Design of the Seasonic G-series 550W

The Seasonic G-series 550W PSU

The G-series 550W power supply looks like a simplistic copy of the Platinum 1000W. The chassis of the power supply conforms to the normal ATX design guide standards in terms of size, yet Seasonic replaced the typical round fan grill with a honeycomb grid. There is no sticker or logo on the oversized fan engine. The entire power supply is sprayed with the matte black paint.

Left Side sticker

A black sticker with the series logo covers the left side of the power supply. There is nothing significant regarding the sticker as it offers little more than aesthetic enhancement.


Right Side sticker

The sticker with the detailed electrical specifications of the Seasonic G-series 550W power supply has been placed on the right side of the chassis, where it is unlikely to be seen inside most cases, with the rare exception of cases which have their PSU compartment both at the bottom of the chassis and upside down.

Rear Side

The G-series units are semi-modular power supplies, therefore there are hardwired cables but also connectors for removable cables at the rear side of the unit. A legend has been subtly printed beneath the connectors. The unit offers the following number of connectors:

Native cables

24pin ATX

4+4 CPU 12V

Modular cables

2 x 6+2 pin PCI-E

5 x Molex

6 x SATA

1 x Floppy*

*Note that the floppy adapter will occupy one Molex connector

Front Side

As is the case with almost all modern power supplies, the front side of the Seasonic G-series 550W is entirely perforated. A typical on/off switch may be found, as well as a blue badge with the company's logo.

A look inside the Seasonic G-series 550W

The cooling fan

ADDA supplies the simple, black 120mm cooling fan found inside the G-Series 550W unit. The model number is AD1212MB-A70GL; a high speed ball bearing fan, capable of reaching up to 2050RPM.

Inside the Seasonic G-series 550W unit

As Seasonic is a company which designs and manufactures not only their own products but units for other brands as well, it is only natural that the G-Series 550W power supply is designed and built entirely by Seasonic alone. An expert can identify the presence of multiple solid polymer capacitors, an LLC resonance converter for increased efficiency and DC to DC conversion circuits. It would appear that Seasonic found a way of mass producing units making use of advanced electronic topologies at a lower cost, which can explain the competitive price of this power supply despite the very modern design.

The filtering stage

A PCB behind the A/C receptacle holds several line filtering components, yet not all of them, with the filtering stage continuing onto the main PCB as well. The filtering stage is very strong, with the total number of components up to six Y capacitors, two X capacitors, three chokes, a MOV and a classic glass fuse.

Primary side

The single bridge rectifier can be seen on its own dedicated heatsink, right after the filtering stage. A single Nippon Chemi-Con KMR 420V/390uF capacitor and a medium sized coil are the primary passive components of the APFC circuit. The active components, two transistors and a diode, can be found attached to the large heatsink across the edge of the power supply. Two transistors form the primary stage inversion circuit, a half-bridge topology, which are mounted on a smaller heatsink right next to the main transformer.

Secondary side

Two transistors and two diodes form the secondary side of this power supply but they are placed on the bottom side of the main PCB. This topology produces only a single 12V output and the 3.3V/5V lines are derived from the DC to DC circuits found on the vertical daughterboards. Most capacitors around the secondary side of this power supply are solid state polymer products from Enesol, yet there are a few classic electrolytic capacitors by Nippon Chemi-Con as well.

Test Setup

The load

In order to be able to effectively and efficiently test any computer power supply unit, we developed and constructed our own proprietary testing station. Our testing station consists of a number of power resistors and small capacitors, which in turn are connected to a RS485 electronic relay array which allow our load to be controlled through computer software alone.

USB interface and connection panel

When accuracy and speed are of critical importance, a simple multimeter or voltage meter is not sufficient for the task. To ensure the quality of our testing, an USB laboratory interface is being used to continuously monitor and record the readings of all voltage lines simultaneously. For ripple measurements, an oscilloscope is necessary and we chose the USB Instruments Stingray, the most widely used oscilloscope amongst low voltage PSU engineers and testers.

Measurement instruments

For accurate testing and repeatable results, a stable power input is also required. Thus, we are providing power to our test samples through a 3kVA VARIAC which allows us to control the input voltage of our test samples and also perform efficiency tests under both 110V AC and 230V AC input. A Lutron DW-6091 is also being used, monitoring the input voltage, real and apparent power, power factor and amperage.

The software

A power supply testing procedure would not be complete without thermal and acoustics tests. For our acoustics tests we are using a SL-5868P digital sound level meter, placed 1 meter away from the unit (DIN standard). Two PT100 sensors and their respective displays are being used to monitor the ambient temperature and the exhaust temperature of the unit.

Complete test setup during trial run


Testing results (Regulation & Ripple)

The electrical performance of the Seasonic G Series 550W power supply is exceptional, especially considering the market it is aimed at. We found the voltage regulation to be more than satisfactory, with the power supply maintaining it at below 1.4% on all of the three voltage lines, while the ripple suppression is nothing short of outstanding, peaking at 26mV on the 12V line under full load and just at 10mV on the two minor voltage lines.

Testing results (Efficiency, Noise & Thermal)


Although the efficiency of the Seasonic G 550W power supply is extremely stable and high while the unit is powered from a 110V AC source, the unit failed to meet the 80Plus Gold certification limit of 92% at half load while it was being powered from a 230V AC source. Nevertheless, the efficiency of this product remains very high, although it appears to be optimized for markets with 90V-120V AC grids.


The mediocre power output and very high efficiency allow for the Seasonic G 550W power supply to generate minimal amounts of heat. Thus, it is no wonder that the thermal performance of the particular unit is astonishing, with the unit getting barely warm under maximum load and the temperature differential between its intake and exhaust is a mere 4.5°C.


The high efficiency of this power supply, in conjunction with the good design and sizable heatsinks, allows for the fan to maintain a low rotational speed, keeping noise down to a minimum. Thus, the Seasonic G 550W will remain entirely silent even if heavily loaded, with the noise coming from the fan getting clearly discernible only of the load exceeds 90% for prolonged periods of time.

Seasonic G Series 550W PSU - Conclusion

Seasonic always aims high with their retail products and the G Series 550W unit is no exception to that rule. Even though it is meant to be a fairly priced high performance product for the mainstream market, Seasonic managed to keep the production cost low while still making use of modern technology.

Seasonic G-550 fan view

We have to admit that the electrical performance of the G Series 550W power supply was much better than we usually expect from similar products. With excellent voltage regulation and even more remarkable ripple suppression, we are certain that the electrical performance of this power supply will satisfy even the most hardcore of users; let alone the casual gamers and advanced users which this power supply is aiming to please. Even the conversion efficiency of the unit is very stable and high, even though the G Series 550W slipped while trying to meet its 80Plus Gold certification standard while being powered from a 230V AC source. Last but not least, those seeking a low-noise product will surely be satisfied by the noiseless operation of this power supply, which can maintain extremely low noise levels while operating up to 80% capacity.

When it comes to aesthetics, we believe that Seasonic did very well considering the class of the G series 550W power supply. The company made this unit semi-modular, installed decorative stickers and a unique fan grill, allowing the power supply to subtly stand out of the crowd without being too fancy or kitschy.

Seasonic G Series 550W main transformer

As we have thoroughly mentioned throughout our review, one of the strongest selling points of the G series 550W unit is the low retail price of the unit. The Seasonic power supply is currently selling for $89.99 shipped, which may not be the lowest price around for an 550W 80Plus Gold certified product, yet it actually is an excellent deal considering the quality, technology, performance, modular design and 5 year warranty coming with the G series unit.

Legit Bottom Line: If you are looking for an excellent high performance power supply as a long term investment on a casual gaming system or any other PC where high reliability but medium levels of power are required, then the Seasonic G Series 550W is likely one of the best choices one could go with.