Seasonic CORE GX-850 (ATX 3) 850W Power Supply: features and specs

The Seasonic CORE GX-850 (model CORE V2 GX-850, ATX3) is an 850-watt internal power supply for desktop PCs. It is 80 PLUS Gold certified, fully modular and ready for ATX 3 and PCIe Gen 5 graphics cards. Here is what those terms mean.

850 watts and 80 PLUS Gold

The 850W figure is the maximum power the unit can deliver to the PC's components. The 80 PLUS Gold certification refers to efficiency: Gold units typically convert at least about 87–90% of the power they draw from the wall into usable DC power at common loads, with less lost as heat. Seasonic describes the unit as high efficiency, with the certification confirming it.

ATX 3 and the 12V-2x6 cable

ATX 3 is the newer power supply standard, designed with modern graphics cards in mind, including their short spikes in power draw. The unit includes a 16-pin PCIe Gen 5 cable (12V-2x6), the connector used by many recent high-end graphics cards. Seasonic lists it as compatible with NVIDIA RTX 40/50 and AMD GPUs. Always plug the connector in fully, as the graphics card and power supply manuals describe.

Fully modular cabling

Fully modular means every cable detaches from the unit. You connect only the ones the build needs, which reduces clutter and improves airflow in the case. Seasonic also lists a cable-free connection design, gold-plated high-current terminals for the motherboard, CPU and PCIe connections, and PVC embossed cables.

Compact 140mm body

The unit is 140 mm long (the listing gives dimensions of about 5.5 x 5.9 x 3.4 inches, 3.5 lb), shorter than many 850W units. That helps in smaller cases and leaves more room for cables.

Cooling and electrical design

The OptiSink design and a 120 mm Hydro Dynamic Bearing (HDB) fan handle cooling. Seasonic specifies tight voltage regulation of ±3% on the 12 V, 5 V and 3.3 V rails and a DC-to-DC converter design, in which the +12 V rail feeds converters for the minor voltages. It also lists ample +12 V output, which matters most because CPUs and graphics cards draw mainly from that rail.

Warranty

Seasonic offers a seven-year warranty. Check the terms with the manufacturer.

Who it suits

It suits builders of mid-range to high-end gaming or workstation PCs who want a graphics-card-ready ATX 3 supply and tidy cabling in a compact case. The right wattage depends on your components, so add up the CPU and graphics card requirements first.

What to check before you buy

• Wattage: compare the 850W output with your graphics card and CPU recommendations, leaving some headroom.
• Case fit: confirm your case takes standard ATX power supplies of this length.
• Connectors: check that the supplied cables match your graphics card, such as the 12V-2x6 or 8-pin connectors.
• Modular cables: use only the cables supplied with this unit, since cable pinouts differ between models.
• Installation: follow the manual and switch the unit off at the wall before working inside the PC.

The short version

• 850W, 80 PLUS Gold, fully modular ATX 3 power supply.
• 16-pin PCIe Gen 5 cable (12V-2x6) for current graphics cards.
• Compact 140 mm body with a 120 mm HDB fan.
• Tight ±3% voltage regulation and gold-plated terminals.
• Seven-year warranty.

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