In the realm of power supply units (PSUs), the core underpinning of any high-performance computing system, seasoned market players have continually raised the bar in delivering efficient, reliable, and technologically superior products. One such stalwart in the PSU domain is SeaSonic, whose meticulous engineering and innovation have repeatedly set industry benchmarks.

In today’s review, we are having a look at the ATX 3.0 upgrade of SeaSonic’s revered Focus series, which epitomizes a fine balance between cost and performance aimed at catering to a broad spectrum of PC enthusiasts and builders. It is the successor of the Focus Plus series, which used to be SeaSonic’s most popular series over the past several years.

The new Focus GX series consists of five units with a power output ranging from 550 Watts to 1.000 Watts. It is the second most powerful unit of the series that we will be putting to the test, the Focus GX-850. SeaSonic is placing its marketing efforts mostly on the exceedingly long 10-year manufacturer’s warranty, its compact size, the 80Plus Gold efficiency certification, and the modular design.

SeaSonic Focus GX-850 ATX 3.0 (SSR-850FX3)
Power specifications ( Rated @ 50 °C )
RAIL +3.3V +5V +12V +5Vsb -12V
MAX OUTPUT 20A 20A 70A 3A 0.3A
100W 840W 15W 3.6W
AC INPUT 100 - 240 VAC, 50 - 60 Hz
MSRP $168

Packaging and Bundle

SeaSonic supplies the Focus GX-850 in a sturdy cardboard box with black-gold artwork based on simple geometric shapes. The PSU is sandwiched between two packaging foam pieces and is placed inside a nylon pouch, ensuring safe shipping.

The bundle accompanying the GX-850 is relatively rich for what is supposed to be a mainstream PSU. Aside from the standard AC power cable and four mounting screws, SeaSonic also provides a number of cable ties, cable straps, a full manual, and a 24-pin connector jumper that can be used to power the PSU without connecting it to a motherboard.

The modular cables of the Focus GX-850 are all identical, with individually sleeved black wires and black connectors. This includes even the 12VHPWR cable, making this the first time we saw a manufacturer changing that particular cable to match the rest of the unit’s cables.

SeaSonic Focus GX-850 ATX 3.0
Connector type Hardwired Modular
ATX 24 Pin - 1
EPS 4+4 Pin - 2
EPS 8 Pin - -
PCI-E 5.0 - 1
PCI-E 8 Pin - 3
SATA - 10
Molex - 3
Floppy - 1

The SeaSonic Focus GX-850 Gold PSU

External Appearance

Despite its ample power provision, SeaSonic has successfully housed the new Focus GX-850 within the conventional ATX dimensions of 150 × 140 × 86 mm (W×D×H), ensuring its compatibility across a broad range of ATX-compliant enclosures, including Desktop HTPC and other compact configurations. The electrical specifications and certifications sticker is located on the top surface of the unit.

SeaSonic typically maintains a minimalist approach towards aesthetics, but the Focus GX-850 stands as a deviation. The design has been elevated beyond mere paintwork, showcasing a distinctive fan grill at the bottom of the chassis. It is adorned with a grey badge at its center and black accents encircling the fan, replacing the previous gold and grey scheme. The embossed geometric motifs on the lateral sides of the PSU have been retained, with the company and series logos subtly highlighted on all faces of the unit.


In addition to the standard small on/off switch and AC cable receptacle, SeaSonic has incorporated a square locking switch on the PSU's rear side. This switch facilitates the management of the cooling fan's hybrid control mode. This mode is activated by default, allowing the fan to engage only when the load escalates to a level necessitating active cooling. When deactivated, the fan’s speed continues to be thermally regulated, albeit without ever coming to a complete halt. The front of the chassis houses the connectors for the modular cables. Although the connectors are not color-coded, a basic legend is imprinted on the chassis to guide the cable connections. The PCI Express and CPU 12V cables utilize identical connectors, negating the possibility of erroneous cable insertion owing to the distinct connector designs and keyed configurations.


Internal Design

SeaSonic once again entrusted the cooling of their Focus series to Hong Hua and their HA13525H12F-Z 120 mm fan. It is a visually simple black fan but features a high-quality Fluid Dynamic Bearing (FDB), with SeaSonic promising high life expectancy and relatively low noise figures. It has a maximum rotational speed of 2000 RPM, an average figure for a 120 mm fan.

SeaSonic is both the designer and manufacturer of their units, negating the need for us to identify an underlying OEM with their products. At first glance, it allows us to realize that, unlike many other manufacturers, SeaSonic’s engineers took major steps in redesigning the platform that the previous Focus series was based upon to fully comply with the ATX 3.0 specification. The unit's interior is extremely tidy, without a single loose cable, as the PCBs are connected via solid copper bridges.

The filtering stage begins on the small PCB at the rear of the AC receptacle and continues onto the main PCB, with a total of four Y capacitors, two X capacitors, and two filtering inductors. Two bridge rectifiers share the same heatsink with half the inversion transistors of the primary stage.

Nippon Chemi-Con supplies the massive 680μF capacitor of the APFC stage, which is placed next to an equally large filtering inductor. The active PCF components, two 6R190P6 power transistors and a diode can be found on the long heatsink across the edge of the PCB.  SeaSonic implemented a full-bridge LLC inversion stage, a rare sight inside a mainstream unit. Two of the power transistors (GPT13N50DG) are on their separate heatsink, and two share the heatsink with the input rectifiers.

On the other side of the transformer and the underside of the main PCB, four IC840L MOSFETs generate the single 12V line. The DC-to-DC converters for the 5V and 3.3V voltage lines can be seen on the vertical daughterboard that also hosts the fan’s controller. The secondary side capacitors are a mix of Rubycon, Nippon Chemi-Con, and Nichicon products, all of which are from Japanese manufacturers.

Cold Test Results (~25°C Ambient Temperature)
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  • RomanPixel - Friday, December 1, 2023 - link

    I bought the MSI MPG Ai1000P from MicroCenter and it has the 12V-2x6 plug. Says so on the box and printed next to the plug on the unit it's self. The cable also has a yellow tip to indicate it's the 12V-2x6, came with a info slip of paper saying so. But MSI's website says it has the old connector. It's like a quiet revision.
  • Counterspeller - Wednesday, November 29, 2023 - link

    Been using Seasonic for years, have a 450W (don't remember the model) in my 10y old 4770, it's still working, used a TX-750 Platinum on my 1900x, using a TX-850 Titanium on this PC. Not 1 has failed.
  • Oxford Guy - Friday, December 1, 2023 - link

    I still have an ultra-cheap Xigmatek PSU from many many years ago that came with a 135mm FDB fan. The PSU still works, too. Why we're still getting 120mm fans in PSUs is beyond me.
  • 120or135 - Friday, December 8, 2023 - link

    is the fan really 120mm?
    says 135mm at their site

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