SeaSonic is a company that hardly requires an introduction, as they are perhaps the best-established designer and supplier of high-performance PC power supply units (PSUs) to this date. Not only they design and market their own products, but they serve as the OEM behind the products of several other known brand names.

Over the past year, the company has been renewing a number of their PSU designs, some almost completely. Among their new designs are the new top-tier 80Plus Titanium certified units and SFX format PSUs. Although we reviewed both of these products in the past and they have left us with very positive impressions, these are ultimately somewhat niche products and the bulk of the market lies elsewhere.

So for today's review we're taking a look at SeaSonic’s latest mainstream market release, the Focus Plus Gold 750FX. As its name suggests, it is an 80Plus Gold certified ATX power supply with a maximum power output of 750 Watts. The Focus Plus Gold 750FX is at its core a product targeting the mainstream market, looking to strike a balance between quality, performance, and value.

*There is a catch with the operating temperature of this model. SeaSonic rates it as operational up to 50 °C but de-rates its power rating down to 80% for temperatures over 40 °C. Therefore, we consider the Focus Plus Gold 750FX to be rated at 40 °C for its rated performance.

Packaging and Bundle

The Focus Plus Gold 750FX ships in an aesthetically simple cardboard box, with its artwork based on basic geometric shapes and focused on a black-gold color theme. Under the thin paper skin of the packaging, we find a strong cardboard box with the PSU well-secured inside it, providing ample shipping protection.

Inside the box, we find a relatively rich bundle for a mid-tier PSU. There are a standard AC power cable and four black mounting screws, several cable ties, three black/blue cable straps with the company logo printed on them, a case badge, and a basic user’s manual.

As the SeaSonic Focus Plus Gold is a fully modular PSU, every cable can be detached, including the 24-pin ATX cable. All of the cables are completely black, made of black wires and black connectors. The smaller SATA/Molex power cables are ribbon-like, or flat-type, but the larger PCI Express and CPU 12V connectors are made of regular wires covered in black nylon sleeving.

External Appearance

Despite its relatively high power output, SeaSonic managed to fit the Focus Plus Gold 750FX into a standard ATX 150 × 140 × 86 mm (W×D×H) chassis. The 140 mm deep body ensures that the Focus Plus Gold 750FX will fit in any ATX-compliant case, including Desktop HTPC and other compact designs. The sticker with the electrical specifications and certifications of the PSU can be found at the top side of the unit.

Although SeaSonic usually is very subtle when it comes to aesthetics, we can safely declare that the Focus Plus Gold 750FX is an exception. The designer clearly went out of their way to make this PSU aesthetically appealing beyond just a good paint job. At the bottom of the chassis, we find a unique fan grill with a golden badge at its center and grey accents surrounding the fan. Embossed geometric designs can be found on the left and right sides of the PSU, while the gold-accented company and series logos can be found on every side.

Besides the typical on/off switch and an AC cable receptacle, SeaSonic also placed a square locking switch on the rear side of the PSU. This switch can be used to enable the cooling fan’s hybrid control mode. Enabled by default, in hybrid mode the fan will turn on only when the unit’s load is high enough to require active cooling. Otherwise if hybrid mode is disabled, the fan’s speed will still be thermally controlled, but it will always run and never go completely fanless.

Meanwhile the front of the PSU is home to the connectors for the modular cables. SeaSonic did not color-code the connectors, but they have a basic legend printed on the chassis that indicates where each connector goes. PCI Express and CPU 12V cables share the same connectors. It is practically impossible for a user to insert a cable into the wrong connector, as each cable type has a different connector and the connectors are keyed.

Internal Design

The cooling fan under the fancy finger guard is the HA1225H12F-Z from Hong Hua. It appears visually simple but features a high-quality Fluid Dynamic Bearing (FDB) with a high life expectancy and promises relatively low noise levels. It has a theoretical rotational speed of 2200 RPM but is thermally controlled and should only actually reach those speeds if the PSU is highly stressed.

There is no need to verify the OEM of this unit as SeaSonic obviously is both the designer and the maker of this power supply. The interior of the unit is very tidy, shouting the obvious lack of wires between the main and the connector’s PCBs, which are joined together via a large copper bridge. The heatsinks are worryingly simple for a PSU of this power rating, suggesting that SeaSonic is very confident regarding its conversion efficiency.

A small PCB is soldered on the back of the AC cable receptacle, hosting a few parts of the filtering stage. The total filtering stage consists of four Y capacitors, two X capacitors, and two filtering inductors. A MOV is also present, as well as an IC that handles the discharging of the filtering capacitors (CM02X). Right after the filtering stage, two bridge rectifiers share the one and only high-density heatsink found in the unit.

The APFC circuit is textbook, with the active components on the thick, crude heatsink across the edge of the PCB. Nippon Chemi-Con supplies the single 400V/560μF capacitor that sits next to a decently-sized enclosed-type filtering coil.

A rare sight these days, the Focus Plus Gold 750FX sports four primary inversion side MOSFETs that form an LLC resonant full-bridge topology. On the other side, another four MOSFETs generate the single 12V line. The DC-to-DC converters for the 5V and 3.3V voltage lines can be seen on the moderately sized vertical PCB that has a heatsink hidden behind it. All of the secondary side capacitors, electrolytic and solid alike, are made by Nippon Chemi-Con.

Cold Test Results

For PSU testing, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M 40 MHz 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.

Right off the bat, the SeaSonic Focus Plus Gold 750FX behaves a little strangely in terms of electrical conversion efficiency. While most designs easily meet the 80Plus efficiency certification requirements at an input voltage of 115V AC – where the standard’s requirements are more lenient – the Focus Plus Gold 750FX greatly surpasses the 80Plus Gold certification requirements with an input voltage of 230V AC, only for the unit to struggle when powered from a 115V AC source. When the input voltage is 230V AC, the average efficiency across the nominal loading range is over 91.5%, an amazing figure for a mainstream PSU. If the input voltage is 115V AC, the efficiency plummets by nearly 3 percentage points across the entire load range, with the PSU barely meeting the 80Plus Gold certification requirements.

The default thermal control mode for the SeaSonic Focus Plus Gold 750FX adopts a semi-fanless cooling strategy, meaning that the fan will start only when it needs to. In our case, the fan started once the load surpassed 215-220 Watts. Naturally, the lack of active cooling under low loads means that the internal temperatures of the PSU will be comparatively higher than those of a full-time actively cooled PSU, but the temperature of the PSU quickly stabilizes one the fan starts. The internal temperatures of the SeaSonic Focus Plus Gold 750FX are mediocre for such an efficient product.

A look at the sound pressure level chart reveals that the active cooling requirements of the SeaSonic Focus Plus Gold 750FX are quite low. The fan does not even start before the load is greater than 200 Watts. When the fan eventually starts, the sound pressure is at practically inaudible levels while the load is below 400 Watts, after which point the thermal controller will keep increasing the speed of the fan in order to cope with the rising cooling requirements of the PSU.

Hot Test Results

The following tables showcase the power quality figures of the SeaSonic Focus Plus Gold 750FX, which generally are very good. The maximum voltage ripple on the 12V line is 30 mV, which is admittedly an unimpressive figure when compared to higher tier modern products, yet it's undoubtfully excellent for a mid-tier product as it's merely 25% of the ATX design guide's recommended 120 mV limit. The filtration of the 3.3V and 5V lines is equally good, with our instruments reading a maximum voltage ripple of 16 mV on the 5V line. Voltage regulation is at about 1% for all three voltage lines, an excellent figure for a product of this class.

The energy conversion efficiency of the SeaSonic Focus Plus Gold 750FX barely even drops when the unit is operating inside our hotbox, indicating excellent resistance to thermal stress. The degradation increases when the load is greater than 600 Watts, suggesting that the components of the PSU are facing some thermal stress, as expected under such high ambient temperatures after reviewing the specifications of the unit. The average efficiency reduction is only 0.5%, with the worst figures being 0.8-0.9% when the load is greater than 600 Watts.

Unlike before, the cooling fan of the SeaSonic Focus Plus Gold 750FX PSU started immediately after we powered on the PSU into our hotbox. Even at the lowest of loads, the fan is now both spinning and audible, with its speed increasing as the load increases. The speed of the fan peaks when the load reaches 600 Watts, maintaining barely operational temperatures under such adverse operating conditions.

Conclusion

Exceptional quality, both internally and externally, is the signature feature of the Focus Plus Gold 750FX. Externally, the designers made sure that the PSU will be aesthetically appealing with a modern, yet not extravagant design. Internally, SeaSonic is using only top-quality components from known and reliable manufacturers – including using only Japanese capacitors – all while the design and assembly of the Focus Plus Gold 750FX are both exceptional. It is no coincidence that SeaSonic backs this unit up with a 10-year warranty, one of the longest offered for a PSU.

In terms of performance, the Focus Plus Gold 750FX is a great all-rounder, yet a master of none. Its greatest characteristic is the excellent acoustics performance, with the PSU operating inaudibly under low-to-regular load when the ambient temperatures are not too high. The power quality of the PSU may be unimpressive when compared to what top-tier PSUs may achieve, yet the figures are undoubtedly admirable for a mainstream product. It does run a little hot considering its power output and electrical efficiency, yet it's not hot enough to cause any issues.

As good as it may perform, there is a catch with the unit’s specifications that we should note – SeaSonic rates the PSU for operation up to 50°C, yet de-rates its power output for temperatures above 40°C. While the Focus Plus Gold 750FX was able to deliver the entirety of its rated power output while operating in our hot box, the platform is only rated for operation up to 40°C, and higher ambient temperatures will severely shorten the unit’s lifetime. Which for most builders shouldn't be a problem, but it could potentially be a concern if you intend to use the PSU in a consistently warm environment without air conditioning.

Overall, SeaSonic is obviously aiming the Focus Plus Gold series at the heart of the advanced PC market, with units that offer ample power output and good performance for the typical gaming/advanced workstation PC while preserving a relatively sensible price tag. The retail price of $110 is reasonable and on par with other high-quality products of comparable performance and quality, making the Focus Plus Gold 750FX an excellent deal for users that want a very reliable, good all-around PSU.