Power Supply Quality

As part of our testing, we also check output parameters are within specifications, as well as voltage ripple and line noise.

Main Output
Load (Watts) 172.62 W 431.07 W 643.7 W 855.58 W
Load (Percent) 20.31% 50.71% 75.73% 100.66%
  Amperes Volts Amperes Volts Amperes Volts Amperes Volts
3.3 V 1.82 3.38 4.56 3.36 6.83 3.34 9.11 3.34
5 V 1.82 5.14 4.56 5.12 6.83 5.09 9.11 5.08
12 V 12.91 12.17 32.27 12.16 48.4 12.11 64.53 12.07


Line Regulation
(20% to 100% load)
Voltage Ripple (mV)
20% Load 50% Load 75% Load 100% Load CL1
3.3V + 5V
3.3V 1.4% 14 16 20 22 16 24
5V 1.2% 16 16 22 24 20 24
12V 0.8% 30 26 30 46 42 36

Most early SFX PSU designs displayed poor power quality figures but, thankfully, all recently released platforms have been greatly improved. The only peculiar characteristic of the FSP Dagger Pro is that the power quality worsens when the load goes below 200 Watts, quite possibly an unforeseen side effect of operating with passive cooling. Regardless, the power quality figures are very good across the entire load range, with the voltage ripple figures below 50% of the recommended design limit. Voltage regulation is equally good, with the 12V maintaining regulation of 0.8% across the nominal load range, which figure goes up to 1.2% for the 3.3V and 5V lines.

As part of our standard testing, we test the primary protections of all PSUs we review (Over Current, Over Voltage, Over Power, and Short Circuit). The FSP Dagger Pro 850W successfully passed all of the tests, generally reacting timely when needed and shutting down to protect itself and the components it is powering. It is noteworthy to mention that the over-power protection (OPP) is set quite low, with the unit shutting down in less than a second when the load is set at 900 Watts. Considering the design and nature of the unit, having the OPP limit set low probably is a good thing for the longevity of the unit itself.


FSP recently updated almost every platform they use in FSP-branded PSUs, and the SFX Dagger Pro series was no exception. With its very compact proportions and massive power output, it is clear that the firm wants to make a serious move towards enthusiasts who build compact but very powerful gaming PCs – a small and yet significant piece of the market.

Not too long ago, it would seem unfathomable for any designer to fit that much power in standard SFX proportions and still keep the cost low enough that the product would be viable for retail store shelves. The inside of the new Dagger Pro 850W PSU definitely is congested but, without question, the firm’s engineers managed to create a clean and workable design. However, sacrifices had to be made in order to fit that much power output in such compact proportions.

The quality of the new Dagger Pro 850W PSU is unquestionably great. It is a well-made unit and the firm is only using top quality components, even for secondary parts. One could argue that they probably had no choice, else the density of the unit itself would threaten its long-term reliability. Regardless, the fact is that the company currently backs the Dagger Pro 850W PSU with a massive ten-year manufacturer’s warranty, underscoring that the PSU is meant to last.

When the Dagger Pro 850W PSU operates under reasonable conditions, its overall performance is good. We received great power quality figures, with exceptional voltage regulation and good filtering. The efficiency is not stellar by today’s standards but does meet the advertised 80Plus Gold certification limits. The combination of extreme power density and the small 92 mm fan did hint at mediocre thermal performance, and that was what we got, with the Dagger Pro getting hot and significantly loud under stress. However, it did not fail to deliver its full power output – not even while it was operating inside our hotbox.

High performance SFX PSUs are slowly but surely gaining ground on the PC market. There are few very powerful SFX units that have two 12V CPU connectors and four PCIe connectors, and as a result there are few direct competitors to the Dagger Pro. On the other hand, enthusiasts who will be building a very compact gaming PC that needs four PCIe power connectors are also very few, meaning that the Dagger Pro is primarily targeted towards a niche market.

Ultimately, with retail prices typically hovering at around $180, the Dagger Pro 850W is priced relatively reasonably given the very high power output of the PSU. Still, it's worth noting that 750W SFX PSUs, including the 750W version of the Dagger Pro, often retail for $30 less and can still power exceptional gaming PCs. So while the 850W version is easy enough to recommend for users who truly need the awesome power of an 850W unit, for most ITX/SFF gaming builds 750W models are a more than reasonable choice that also saves some money in the process.

Hot Test Results (~45°C Ambient)
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  • Oxford Guy - Friday, September 16, 2022 - link

    Small form factors and high wattage are generally mutually exclusive, unless you have impaired hearing and no tinnitus.

    'The use of a low-profile 92 mm fan inside such a compact unit with significant thermal losses did have the expected side effect of high audible sound pressure levels.

    Once the fan starts, it quickly becomes clearly audible, with the noise staying within relatively comfortable boundaries up to about 500 Watts.'

    So, maybe these companies should start calling these units 500W models rather than 850.
  • meacupla - Sunday, September 18, 2022 - link

    The only reason to get an 850W for SFX PSUs, is so that the PC won't crash when an RTX 3080Ti, or something as power hungry, causes a massive transient spike.
    You could probably get away with a 750W ATX PSU, but SFX PSUs are known for not handling transient spikes as well as ATX.
  • Harry_Wild - Monday, September 26, 2022 - link

    Looking for a rectangle shape for my Lenovo Workstation SFF desktop! 850W would be great! $170.00 …sold!
  • shamaizas - Saturday, October 15, 2022 - link

  • shamaizas - Saturday, October 15, 2022 - link

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