I have a bit of an affinity for small, compact cases, and sadly, with a smaller case, you need a power supply that can deliver the power in a small form factor. Enter NZXT’s C850 SFX Gold, a relatively capable PSU with modularity, all in an incredibly compact package, ready for your custom stream-machine-style PC or other ITX builds.
Judging by the marketing, the NZXT C850 SFX Gold is one of the brand’s most compact power supplies yet, and it arrives as a purpose-built solution for anyone trying to push serious GPU power through a shoebox-sized chassis. After testing it in some builds, I have to say it lives up to the hype, if you can look past the price tag.
At first glance, the C850 SFX Gold’s dimensions, 125 x 63.5 x 100 mm, make it hard to believe it can push 850 watts continuously. Normally, you have a pretty heavy unit that is jam-packed with components to deliver that level of power, but NZXT does it in a very small package. That skepticism fades quickly once you start looking at what NZXT has actually packed inside.
Packaging is clean and very on-brand, arriving in the classic NZXT white-and-purple colour scheme. Inside, the PSU is nestled between form-fitted corrugated cardboard, and the included modular cables are tucked away in a branded purple nylon bag. It is a small touch, but a genuinely useful one for storing extras you are not using. It comes with everything you need, but with a PSU, it is all about how well it is built and what power it can deliver.
The cable set covers all the essentials: a 24-pin ATX cable, 350 mm, a 4+4-pin CPU EPS cable, 470 mm, a 6+2-pin PCIe cable, 470 mm, a 16-pin to dual 8-pin PCIe adapter, a native 16-pin 12V-2×6 PCIe 5.1 cable rated for 600W, two SATA cables with three connectors each and a peripheral cable. Notably, the lengths are intentionally short. NZXT made these cables with SFF enclosures in mind, where every millimetre counts. Anyone hoping to repurpose this unit in a full ATX tower might run into some trouble, but that is not the audience here, and these short cables make sure everything fits without it looking like a rat’s nest when it is all together.
Every cable features individually embossed wiring with pre-installed cable combs, which makes a real difference in the chaos that compact builds can quickly become. It is relatively well-positioned and offers a wide degree of flexibility, especially given the size of everything. NZXT packed a lot in this small box, and I am genuinely pleased with the level of quality up to this point.
The C850 SFX Gold is fully ATX 3.1 and PCIe 5.1 compliant, rated at 850W continuous output at up to 50 C ambient. It runs on a single 12V rail rated at 70.83A, with 3.3V and 5V combined up to 100W and a 5VSB rail at 3A, or 15W. Active power factor correction reaches up to 0.97. Protections include OVP, UVP, OCP, OPP, SCP, SIP and OTP, alongside a 100,000-hour MTBF rating at 25 C.
“…in testing, the NZXT C850 SFX Gold lives up to the promise it makes on the box.”
Cooling is handled by a 92 mm Hong Hua fluid-dynamic bearing fan rated at up to 3,500 RPM, 57 CFM, and 41 dBA at maximum speed. All capacitors are Japanese 105 C-rated electrolytics, and the topology features APFC with a double-forward primary design. The unit carries 80 Plus Gold, Cybenetics Platinum efficiency and a Cybenetics A- noise rating. The warranty is 10 years.
For anyone who does not dig deep into each PC component, that is a lot of numbers and specs to take in, but suffice it to say, in testing, the NZXT C850 SFX Gold lives up to the promise it makes on the box. At 50 percent load, the unit hits around 92.12 percent, comfortably exceeding the 80 Plus Gold standard and actually brushing up against Platinum territory. Even at 10 percent load, it pulls 88.97 percent, and at the full 850W, it stays at 86.55 percent.
For everyday gaming loads, which typically land well under the unit’s ceiling, that efficiency translates to lower heat generation, quieter operation and, over the long haul, meaningfully lower power bills. Testing with a range of uses, including gaming with titles such as Doom Eternal, Cyberpunk 2077, Diablo IV and Returnal, on a system with an AMD Radeon RX 9070 XT and a Ryzen 9 9900X, the system stayed consistent with power delivery across all benchmarks and tests. The PSU stayed well within range, and it managed to keep the fluctuations to an absolute minimum.
Speaking of fluctuations, the NZXT C850 SFX Gold also delivers on voltage regulation, which is important when you are dealing with incredibly expensive components. The NZXT C850 SFX Gold sits at 12.18V at 10 percent load and holds at 12.02V all the way to full load, an incredibly small fluctuation, especially when you consider how much power is flowing through this unit. This level of regulation matters when you are running a high-end GPU like an NVIDIA RTX 5080 or RTX 5090, which is sensitive to power fluctuations and can be damaged if things fluctuate too much. It is one area where the C850 SFX Gold clearly punches above its weight class.
On the cooling side, the C850 SFX Gold ships with a Zero RPM mode that keeps the fan completely off at roughly 20 to 30 percent load. Between 25 and 50 percent, it stays at or below 33.7 dBA, barely perceptible in a typical room. That covers many common gaming and productivity scenarios where power draw sits comfortably in the 200W to 450W range.
Once demand climbs past 75 percent, the fan spins up noticeably, reaching 41.6 dBA at full load. That is not unusual for an SFX design, as a 92 mm fan simply has to spin harder than a 135 mm or 140 mm fan would in a full-size ATX unit to move the same volume of air through a much smaller housing.
Now, this level of power does come at a cost, especially when you are talking about an SFX-style unit, but NZXT manages to be pretty competitive, all things considered. At US$169.99 in North America, or around C$208 in Canada, the C850 SFX Gold sits around where most of its rivals are. The Cooler Master V850 SFX Gold lands at around US$144.99, the Corsair SF850 comes in around US$178.99, and the Lian Li SP0850P Platinum 850W SFX sits at roughly US$150. That puts the C850 SFX Gold around the middle of the pack, all while delivering solid construction, fantastic features and some smart design choices that help make it stand out.
That said, there are a few things to consider when looking at the C850 SFX Gold: there is only a single 4+4-pin CPU power cable, no rear power rocker switch and audible noise under sustained heavy workloads. For the primary use case, a Mini-ITX or SFF build with a current-generation flagship GPU, none of those things are particularly limiting. Most compact boards feature only one EPS connector, but it is worth noting, especially if you are looking for flexibility to future-proof your next build.
Even with those minor complaints, the NZXT C850 SFX Gold does exactly what it sets out to do, and does it well. It delivers clean, efficient, ATX 3.1-ready power in a form factor that was, not so long ago, seen as a compromise. The build quality is strong, the electrical performance is tighter than the 80 Plus Gold badge implies, and the cable management situation is genuinely well thought out for the audience it is aimed at. If you are putting together a compact, high-performance gaming rig and want a power supply that will last, the NZXT C850 SFX Gold is a very easy addition to any parts list
- DESIGNED FOR COMPACT BUILDS — Maximize space efficiency with the SFX form factor, delivering full-power capabilities in a size optimized for small form factor (SFF) cases.
- RELIABLE GPU POWER — ATX 3.1 certification and a 600W 12V-2×6 connector ensure safe, dependable power delivery for modern graphics cards.
