FSP Dagger Pro 850W SFX PSU review: The 80 Gold Plus standard of compact power supplies

Small PSU that packs a punch.

FSP Dagger Pro 850W
(Image: © Rich Edmonds / Windows Central)

Have you ever heard of FSP? It's a brand that isn't particularly renowned for making the best power supplies, but the company actually does just that by making PSUs for the likes of EVGA, Cooler Master, among others. We're big fans of EVGA hardware and so were excited to get hold of FSP's own Dagger Pro SFX PSU.

Small form factor (SFX) power supplies are designed for use in more compact PC cases. The major difference between SFX and full ATX power supplies is size. SFX units usually come in at 125mm x 100mm with a height of just 63.5mm. That's precisely where you'll find the FSP Dagger Pro 850W SFX PSU we have for review today.

FSP Dagger Pro 850W: Price and availability

FSP Dagger Pro 850W

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

You can find the FSP Dagger Pro 850W SFX PSU for around $200. This is quite the hefty price to pay for the capacity, but this is the cost of SFX PSUs, which often command premiums compared to standard, larger ATX units. It's a pretty good listing price to put it in line with competitor products, including the excellent SilverStone SX800-PT.

FSP Dagger Pro 850W: Tech specs

  • Capacity: 550W, 650W, 750W, 850W
  • Dimensions: 125mm x 63.5mm x 100mm
  • Type: Modular
  • Fan: 92mm, fluid bearing
  • Efficiency rating: 80 Plus Gold
  • Voltage regulation: ±%
  • PCIe ports: 2
  • Operating temp: Up to 40C (104F)
  • Safety: OCP, OVP, SCP, OTP, OPP
  • Warranty: 7 years
  • Manufacturer: FSP

There's plenty to like here with the Dagger Pro 850W. While under-volt protection (UVP) isn't present, FSP has implemented its own patented voltage controller and uses high-quality Japanese capacitors for a premium build. It's rated for delivering up to 54A on the single +12V rail and is capable of running up to 40C with an 80 Plus Gold efficiency certification.

FSP Dagger Pro 850W: What's good

FSP Dagger Pro 850W

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

FSP makes some great PSUs for other brands and so we expected to see some excellent performance from the SFX series of FSP Dagger Pro power supplies. The range starts at 550W and goes up to 850W in increments of 100W, providing a strong choice for anyone looking to build a compact PC.

550W is still good enough for many PC builds, though 650W should be considered for RTX 30-series graphics cards. The unit we received for review was the range-topping 850W. It rocks a single 12V rail that can handle up to 54A of power draw, which is more than enough for even more enthusiast-grade components.

Matching the SFX standard dimensions, you'll have no issues fitting the FSP Dagger Pro SFX PSU into the most compact PC cases. In terms of safety, which is incredibly important since this is what will be handling the conversion of electricity for all your PC parts, FSP included most safeguards aside from under-voltage protection.

FSP Dagger Pro 850W

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

The 80 Plus Gold certification only really determines the level of efficiency a PSU should achieve. The Dagger Pro we're reviewing here is 80 Plus Gold, which means it should be around 92% efficient at 50% power load, which is where you should aim for with your PC components. The less heat waste produced, the less power required from the wall.

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Load80 Plus Bronze80 Plus Silver80 Plus Gold80 Plus Platinum80 Plus Titanium

80 Plus Titanium is about as good as you will get from consumer power supplies and Gold is pretty much slap-bang in the middle. But looking at the table above, the actual differences between each grade are small. FSP includes the following cables with the Dagger Pro SFX:

  • 1x 24/20-pin ATX
  • 1x 8/4-pin EPS/ATX 12V
  • 1x 8-pin EPS/ATX 12V
  • 2x 8/6-pin PCIe

I also appreciated the SFX to ATX bracket included with the PSU, just in case you needed to use it inside a larger PC case. The majority of PSUs we test pass with flying colors, and while we could go all-out with a digital oscilloscope to really dig deep into the power figures, so long as the unit is able to perform reliably in real-world conditions, that's what really matters to consumers.

The FSP Dagger Pro 850W SFX lets you build a powerful compact gaming PC.

This is why we don't go too in-depth, especially with power supplies. How we test units involves connecting one to a reasonable load and seeing how it performs in a variety of test scenarios to represent how they would be used by owners. After putting the Dagger Pro 850W SFX to the test in a system with an AMD Ryzen 9 5950X CPU and NVIDIA GeForce RTX 3080 GPU, we encountered no issues.

The test bench was used to process and render video, run synthetic benchmarks for prolonged periods of time, and play some demanding games like Grand Theft Auto 5, Cyberpunk 2077, and Mount & Blade II: Bannerlord. The power supply fan kicked in, but it's barely noticeable over two fans running to keep the Ryzen 9 processor cooled with an AIO. Software monitors showed stable power delivery to the most critical components, which was expected and is great news for the PSU.

FSP Dagger Pro 850W: What's not good

FSP Dagger Pro 850W

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

There's not really much to dislike about the Dagger Pro 850W. In terms of pricing, it's expensive for a PSU, but it's in line with the competition, if not more affordable. For 850W of stable power in a compact form factor, you should expect to pay a small premium. The fan can also ramp up and make some noise, though you'll be hard-pressed to hear it during normal operation.

FSP Dagger Pro 850W: Competition

SilverStone SX700-PT

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

A close contender to the FSP Dagger Pro is the SilverStone SX range of SFX PSUs. We reviewed the SilverStone SX700-PT, which was very good thanks to the high-quality components and excellent performance. It was let down by the limited warranty and 85C-rated capacitors.

FSP includes a seven-year warranty with the Dagger Pro 850W, which is pretty good at this price range. It too also has high-quality Japanese capacitors, which is what you want at this price. The fan is good enough to keep the temperatures down, even when going all-out with upwards of 600W of power draw.

The SFX market of PSUs is a little more limited than full-size ATX units, but there is a solid choice out there with these two PSUs as fine examples.

FSP Dagger Pro 850W: Should you buy it?

FSP Dagger Pro 850W

Source: Rich Edmonds / Windows Central (Image credit: Source: Rich Edmonds / Windows Central)

You should buy this if ...

  • You're building a PC inside a small form factor case
  • You plan on using a modern GPU
  • You need a PSU to provide clean and stable power

You shouldn't buy this if ...

  • You need to use two or more GPUs
  • You want to spend money wisely
  • You'd prefer a longer PSU warranty

The FSP Dagger Pro 850W PSU is a great option for anyone wanting to put together a compact PC. If you plan on using a smaller PC case that only takes an SFX or SFX-L PSU, you'll need to use such a power supply. You can do much worse than the Dagger Pro 850W, and it's absolutely possible to choose a unit from an unknown brand that runs the risk of frying your expensive components.

You've got the choice of 550W, 650W, 750W, and 850W capacities, which makes this a good choice for modern GPUs like NVIDIA's RTX 30 series. The 80 Plus Gold certification means you can expect to enjoy high levels of efficiency that result in less waste heat inside the chassis and lower power consumption at the wall.

Running an AMD Ryzen 9 5950X and ASUS Strix RTX 3080 saw no problems with the FSP Dagger Pro 850W. The fan spun up under heavy loads in more demanding games or stress testing, but when compared to the overall noise emitting from the system, you won't notice it too much. Overall, this is one stable power platform for even more enthusiast builds.

Rich Edmonds
Senior Editor, PC Build

Rich Edmonds was formerly a Senior Editor of PC hardware at Windows Central, covering everything related to PC components and NAS. He's been involved in technology for more than a decade and knows a thing or two about the magic inside a PC chassis. You can follow him on Twitter at @RichEdmonds.