Seasonic CORE ATX 3 GX-850 power supply review

Seasonic, a well-established leader in power supply technology, is known for its dedication to producing high-quality PC power supply units (PSUs). With a long-standing reputation for reliability and efficiency, Seasonic has consistently delivered products tailored to a broad range of users, from professionals requiring stable performance to gaming enthusiasts seeking durable and efficient power solutions. Unlike many competitors, Seasonic designs and manufactures its own platforms, ensuring a high level of quality control and innovation.

We examine the Seasonic Core GX-850 ATX 3, a revision of the Core series that integrates ATX 3.1 and PCIe 5.1 compliance, to see if it belongs among our list of best power supplies. This model integrates Seasonic’s new OptiSink design, which enhances thermal performance and reduces material usage by optimizing heat dissipation in the APFC and primary inversion circuits. Rated at 850W at 50 degrees Celsius and 80Plus Gold certified, the Core GX-850 ATX 3 aims to balance efficiency, build quality, and affordability.

Specifications and Design

In the Box

The Seasonic Core GX-850 ATX 3 comes in sturdy packaging with the brand’s familiar black-and-gold theme. The PSU is well-protected within a nylon pouch and secured by foam inserts, ensuring safe transit.

Seasonic includes a comprehensive accessory bundle, featuring mounting screws, an AC power cable, cable ties, and three quality cable straps, covering the essentials for installation and cable management.

The Core GX-850 ATX 3 features all-black, individually sleeved cables, offering both aesthetic appeal and flexibility for easier routing. The PSU provides one 12+4 pin PCIe 5.1 connector and three 6+2 pin PCIe connectors, which is a reasonable configuration for its power rating. However, it includes only six SATA and two Molex connectors.

External Appearance

Seasonic made some effort to make this unit aesthetically appealing but did not spend a significant number of resources on it. The Core GX-850 ATX 3 features a sleek, minimalistic design with a satin black chassis and a smooth, high-quality finish that is very resistant to fingerprint marks. The company logo and Core GX branding are etched on both sides and the front.

The unit follows the ATX standard length of 140mm, making it compact enough to fit into virtually any ATX-compatible case while leaving ample room for airflow in tighter builds. The fan grille is integrated directly into the chassis, forming a distinctive visual pattern.

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At the rear, the PSU houses a standard AC input socket and an on/off power switch. The front panel features modular cable connectors with a subtle legend assisting users in correctly connecting their cables during installation.

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Internal Design

The Seasonic Core GX-850 ATX 3 is equipped with a 120mm Hong Hua HA1225H12F-Z fan that employs a fluid dynamic bearing (FDB) for a reliable, low-noise operation. Unlike designs featuring zero-RPM modes, this fan runs continuously - operating at a low speed under light loads and ramping up as the load increases - to ensure consistent thermal management. An FDB fan would not be our first choice for a unit that keeps the fan running all the time but we trust that Seasonic’s engineers are experienced on such matters.

Engineered as an entirely in-house platform, the Core GX-850 incorporates Seasonic’s innovative OptiSink design. OptiSink places the majority of heat-generating components on a dedicated daughterboard before the main transformer, reducing the space needed for heatsinks. This approach aids in heat dissipation and reduces the PSU's overall footprint.

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The input filtering is good for an 850W unit and consists of four Y capacitors, two X capacitors, and two inductors, providing effective suppression. Two rectifying bridges on a fairly large heatsink take care of the primary inversion stage. The Active Power Factor Correction (APFC) stage components are mounted on the OptiSink PCB, with the passive components being a single encased inductor paired with a Teapo 470 μF capacitor.

For the primary inversion stage, four Huajing CB13N50 MOSFETs are arranged in a full-bridge LLC configuration on the OptiSink PCB. On the secondary side, four Leadpower 45013 MOSFETs are positioned immediately after the transformer and cooled by a pair of tall heatsinks to generate the main 12V rail. As expected, dedicated DC-to-DC circuitry on a vertical daughterboard supplies the 3.3V and 5V outputs, with all secondary capacitors sourced from Teapo. The internal design of the Core GX ATX 3 unit is very similar to that of the latest Focus GX series, with the vital differences being the lack of hybrid fan control and the (significantly) inferior quality of its internal components, active and passive alike.

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Cold Test Results

Cold Test Results (25°C Ambient)

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M 40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts.

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During cold testing, the Cooler Master X Silent Edge Platinum delivered an average nominal load efficiency of 90.8% at 115 VAC and 92.4% at 230 VAC, meeting the 80Plus Platinum certificaDuring cold testing, the Seasonic Core GX-850 ATX 3 meets the 80 Plus Gold efficiency certification standards with a 115V AC input, achieving an average efficiency of 89.3%. This increases to 91.6% with an input voltage of 230 VAC but the maximum load efficiency would deny this unit a Gold rating from CLEAResult. Cybenetics does not certify this unit at the time of this review. The highest efficiency is observed around 50% load, aligning well with expectations for modern PSU designs. Efficiency at extremely low loads is fair but could see minor improvements.

The 120mm fan in the Core GX-850 remains active at all times but operates at very low speeds under light to moderate loads. It sharply increases its speed beyond 700W, becoming more than moderately audible. Nevertheless, even when pushed to full capacity, the fan never reaches its maximum speed. Throughout testing at room temperature, the unit maintains relatively low internal temperatures, indicative of the OptiSink effectiveness.tion requirements. At 115 VAC, the unit qualifies for CLEAResult Platinum certification, while at 230 VAC it narrowly misses the 94% efficiency threshold at 50% load. Notably, the unit peaks at 94.1% efficiency at 60% load, which highlights the weaknesses of the CLEAResult efficiency certifications. Cybenetics, whose certification is largely based on average efficiency, awarded the X Silent Edge Platinum a Platinum certification across all input voltages, as well as their best noise certification—a natural outcome of its completely fanless design. The thermal performance is consistently linear throughout the test range, with internal temperatures maintained within safe limits despite the absence of active cooling.

Hot Test Results

Hot Test Results (~45°C Ambient)

During hot testing, the Seasonic Core GX-850 ATX 3 exhibits a significant decline in efficiency due to elevated ambient temperatures. With a 115 VAC input, the unit averages 87.7% efficiency, while at 230 VAC it achieves 90%. These values represent a decrease of approximately 1.6% compared to the cold test results of 89.3% and 91.6%, respectively. This reduction under high-temperature conditions remains within acceptable performance limits but is fairly high, with some evidence of thermal stress under heavy loads.

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The fan is quiet at first but linearly increases its speed alongside with the load, reaching its maximum speed when the load is just shy of 800 watts. The Core GX-850 ATX 3 does get loud under these operating conditions when heavily loaded. On the other hand, internal temperatures are well-regulated, ensuring that the unit stays safely within its thermal limits and far from triggering any over-temperature protection.

PSU Quality and Bottom Line

Power Supply Quality

The Seasonic Core GX-850 ATX 3 exhibits exceptional electrical stability and power quality within its class. Voltage regulation is precise, with the 12V rail maintained within 0.7%, the 5V rail within 0.9%, and the 3.3V rail within 0.8%. Ripple suppression is fairly well-executed, with maximum ripple levels measuring 42 mV on the 12V rail, 26 mV on the 5V rail, and 22 mV on the 3.3V rail. While the overall filtering performance is very good for an 850W unit, there is room for improvement.

During our thorough assessment, we evaluate the essential protection features of every power supply unit we review, including Over Current Protection (OCP), Over Voltage Protection (OVP), Over Power Protection (OPP), and Short Circuit Protection (SCP). All protection mechanisms were activated and functioned correctly during testing.

The OCP thresholds are set very high, even for an ATX 3.1-compliant unit, triggering at 146% for the 3.3V rail, 150% for the 5V rail, and 136% for the 12V rail, while the OPP engages at 138%.

Bottom Line

The Seasonic Core GX-850 ATX 3 is a fairly robust power supply unit that Seasonic designed to compete in the mainstream market. The unit is aesthetically appealing without being extravagant and adheres to the ATX standard with a compact 140mm length, ensuring broad compatibility with most cases. Integrating Seasonic’s innovative OptiSink design, the unit optimizes thermal management by relocating heat-generating components onto a dedicated daughterboard. While its overall design and features are very similar to those of the higher-quality Focus GX series, the Core GX-850 employs somewhat lower-grade internal components. Though this results in a marginal reduction in overall quality, the power supply still maintains dependable performance and meets 80Plus Gold certification standards—all at a price point of $130, which may be considered steep by some.

Electrically, the Core GX-850 demonstrates commendable stability and power quality within its class. The unit delivers precise voltage regulation and effective ripple suppression, with maximum ripple levels recorded at 42 mV on the 12V rail, 26 mV on the 5V rail, and 22 mV on the 3.3V rail. Despite the slightly lower quality of some internal components compared to the Focus GX series, the Core GX-850 still provides excellent filtering and consistently clean power output. Its protection mechanisms are set at relatively high thresholds, which is not due to the components used but rather a design feature.

Thermally, the Core GX-850 performs reliably under both cool and elevated ambient conditions. In cold testing, the PSU achieves very good efficiency levels, maintaining an average conversion efficiency of 89.3% at 115V AC and 91.6% at 230V AC, while keeping internal temperatures low. Its 120mm Hong Hua HA1225H12F-Z fan operates continuously, maintaining quiet performance under most of the load range. Under hotter conditions, efficiency drops measurably (to 87.7% at 115V AC and 90% at 230V AC), with the fan speed surging at a lower load threshold and reaching maximum speed near 800W. Despite the increased acoustic output under heavy loads, the PSU’s effective thermal design ensures safe operating temperatures throughout.

In summary, the Seasonic Core GX-850 ATX 3 offers a balanced blend of reliability, efficiency, and robust power quality. While it mirrors many of the design philosophies of the Focus GX series, it compromises on internal component quality and lacks features like hybrid fan control. Nonetheless, it delivers stable electrical performance, effective thermal management, and acceptable noise levels under load. At $130, the unit is positioned at a premium price point that is dangerously close to the significantly better Focus GX alternative but can quickly become a great deal if found on a sale.

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