Introduction

We would like to thank Seasonic for supplying the review sample.


Seasonic recently released an SFX PSU with 750 W maximum power output in an attempt to dethrone the mighty Corsair SF750 Platinum, which is the best currently available SFX PSU offering. A significant advantage the SPX-750 has over the SF750 is the long 10-year warranty, as the Corsair offers 7 years for its flagship SFX offering. In my opinion, anything above five years is unreasonable when it comes to power supplies, which are highly dependent on the quality of the mains grid, and external factors can affect the latter (e.g., thunderbolts). If a power surge or brownout damages your PSU, the warranty won't cover it, which is reasonable because PSU manufacturers are not responsible for the power grid's quality.

The SPX-750 uses a fully modular cable design with enough EPS and PCIe connectors to support a potent gaming system. It is 80 PLUS and Cybenetics Platinum certified for efficiency and Cybenetics Standard+ certified for noise output. The cooling fan measures 92 mm across and uses a fluid dynamic bearing. It also has a semi-passive operation. With a street price of $190 to $200, it isn't affordable, so it will have to deliver top performance and reliability to justify its high price tag. As this is written, the Corsair SF750 is slightly more affordable as this is written.

This is the first desktop PSU with fan failure protection I have come across. In other words, if the fan has a problem or the PSU doesn't detect it, which would happen if it isn't connected, the SPX-750 won't start.

Specifications

Photos

The box is small, and on the front is the series description, and model number in smaller font. The ten-year warranty is also highlighted. On the back are more details about the product and its specifications.


Protection inside the box is perfect, and the PSU comes in a bag, which is a nice detail. Another bag stores the modular cables. The bundle is rich, including Velcro straps, zip ties, an SFX to ATX adapter, and all the necessary fixing bolts. There is also the user manual and a piece of paper offering the chance to win a $50 Steam gift.


The fan grille follows a nonrestrictive design. The front exhaust grille uses the typical honeycomb design. Below the C14 AC receptacle is the power switch. Unfortunately, there is no switch for toggling on/off the PSU's semi-passive operation.


The unit's series description and Seasonic's logo are on the sides. The power specifications table is on the bottom.


The modular panel has nine sockets.


Dimensions are compact since it follows the SFX form factor.

Cables and Connectors

All cables are short because this PSU is for a small chassis. It does come with an SFX to ATX adapter, which is rendered useless by the short cables if the PSU is installed into a standard-sized chassis. It is good to see 16AWG gauges on cables that can carry lots of power, and the lack of in-cable caps is good as well.


This SFX PSU having two EPS connectors on dedicated cables is great. There are also two PCIe connectors on pretty long dedicated cables. The other two PCIe connectors are installed on a single cable.


The peripheral connectors are adequately far apart for an SFX unit, and there are enough.

Component Analysis

Before reading this page, we strongly suggest looking at this article, which will help you better understand the insides of a PSU.



The small PCB is packed with parts on the primary side, but there is enough space between parts on the secondary side. It is always impressive to see such compact power factories. In SFX PSUs, engineers have to increase power output without sacrificing efficiency, reliability, and output noise. The build quality looks good, and as per usual, Seasonic used topnotch parts.


The transient/EMI filter stages have all the necessary parts.


The MOV should be covered in heat shrink to be kept in place if it blows up.


An NTC thermistor provides inrush current protection by lowering start-up currents.


The bridge rectifier is bolted to the primary heatsink, and it is powerful, able to handle up to 25 A.


The APFC converter uses one Infineon FET and a boost diode by the same manufacturer. The bulk cap is by Rubycon and doesn't have enough capacity to provide a hold-up time of over 17 ms.


The APFC controller is a Champion CM6500UNX.


The two main switching FETs are installed in a half-bridge topology, and an LLC resonant converter is used for higher efficiency. The LLC resonant controller is a Champion CU6901VPA, which uses the burst-mode (Champion calls it kick mode) operation for increased efficiency at super-light loads.


The driver IC for the primary switching FETs is a Silicon Labs Si8230BD.


The unit's main transformer isolates the primary and secondary sides, among others.


The FETs regulating the +12 V rail are installed on the solder side of the main PCB.


The few electrolytic caps are of high quality. Seasonic mostly used polymer caps to filter ripple.


Two DC-DC converters generate the minor rails. They are installed on a daughter board that also hosts the fan's header.


The controller handling both DC-DC converters, generating the minor rails, is an ANPEC APW7159C.


The 5VSB circuit uses an EM8671A PWM controller, and the rectifier on the primary side is an Infineon FET.


There are two supervisor ICs, a Weltrend WT7527RA, which handles the usual duties, and a Weltrend WT51F104 microcontroller responsible for the firmware OPP and OTP. The typical hardware OPP is designed to trip at high power spikes lasting for nanoseconds, while firmware OPP handles lower power spikes that last longer, in the millisecond range. Seasonic doesn't advertise this feature, which is odd as it is a notable advantage over competing offerings.


Several polymer caps are installed on the face of the modular PCB.


Soldering quality is good.


The cooling fan is by Hong Hua. It measures 92 mm across and uses a fluid dynamic bearing.

Test Setup