Best power supply for a two-GPU inference box

Which PSU should you buy for two GPUs?

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For two RTX 3060-class cards, choose the MSI MAG A850GL PCIE5: its 850 W covers the 675 W budget below. Give each card its own PCIe cable. A separate PCIe 8-pin cable goes from its own PSU socket to a card; two plugs sharing one cable still count as one cable.

Choose the Seasonic FOCUS GX-850 if you need a third separate PCIe cable.

For two RTX 3090s, the 850 W options fall short of our 1,125 W budget. The Corsair HX1500i (2025) covers it, including at its 1,200 W rating at 100–115 V input; check your exact cards.

Research note: These are vendor specifications and example budgets, not our own PSU tests. Confirm the exact model, condition, included accessories and seller terms on Amazon before buying.

The buying comparison

PSU / exact version	Rated DC output	ATX / PCIe version	Included GPU connections: 16-pin; legacy 6+2 ends / independent runs	Vendor-listed efficiency certification and body	Warranty
MSI MAG A850GL PCIE5, current version	850 W total; 846 W on +12 V	ATX 3.1 / PCIe 5.1	1 × 600 W 16-pin cable, advertised as 12V-2x6; 4 ends / 2 runs	80 PLUS Gold — CLEAResult; Cybenetics Gold — Cybenetics	10 years, limited
Seasonic FOCUS GX-850 ATX 3.1, v4	850 W total; 840 W on +12 V	ATX 3.1 / PCIe 5.1	1 × 12V-2x6 cable; 3 ends / 3 runs	80 PLUS Gold — CLEAResult; Platinum — Cybenetics	10 years
Corsair HX1500i (2025), CP-9020309-NA	1,500 W at 115–240 V input; 1,200 W at 100–115 V	ATX 3.1 / PCIe 5.1	2 × 12V-2x6 cables, each using two PSU-side 8-pin sockets; 5 legacy ends / 5 runs	80 PLUS Platinum — CLEAResult; Platinum — Cybenetics	10 years

Sources are the exact MSI datasheet and cable diagram, Seasonic datasheet and model-specific cable table, and Corsair’s 2025 power and cable tables. MSI’s US store states its limited warranty.

Allocate the actual PSU sockets for the required cable arrangement; the supplied cable inventory does not mean every alternative cable can be connected simultaneously.

Worked budgets: two 3060s versus two 3090s

NVIDIA’s reference specifications list 170 W graphics-card power for the RTX 3060 and 350 W for the RTX 3090. Use the actual board manufacturer’s specifications when they differ. These figures describe graphics-card power, not the recommended PSU for the whole PC.

For illustration, choose 200 W for everything else and add a 25% reserve to the resulting steady DC budget. Both are planning assumptions; replace them with requirements for the actual CPU, platform, drives, cooling and simultaneous work. The reserve is not a tested transient allowance or a manufacturer approval.

Illustrative configuration	GPU subtotal	Chosen platform allowance	Steady subtotal	With chosen 25% reserve	Supplied-cable target
Two 170 W reference RTX 3060s	340 W	200 W	540 W	675 W	2 independent 8-pin feeds if each board needs one
Two 350 W reference-style RTX 3090s	700 W	200 W	900 W	1,125 W	4 independent 8-pin feeds for two documented 2-input adapters/cards

The two 850 W units clear the first nominal budget and fail the second. A suitable 1,200 W unit would clear the second static calculation; 1,500 W is not a universal minimum. The Corsair is the verified buying option here because its documented output and included cable arrangement address that example together. Still check rail limits, temperature/input conditions, startup and transient requirements against the complete configuration.

Do not add single-card whole-system PSU recommendations together. Do not add another slot-power allowance on top of full graphics-card power. A software cap is a workload setting, not evidence that every startup or driver-reset state stays inside the tuned limit.

Two single-8-pin cards: MSI

Choose the MSI when the complete build fits the 675 W example budget and each card needs one separate PCIe cable. Its four legacy connector ends are on two cables, so count cables rather than plugs.

Give each single-input card its own cable rather than counting plugs as separate feeds.

The current product documentation advertises ATX 3.1 and PCIe 5.1; the checked Amazon offer explicitly describes a 12V-2x6 cable. Some specification rows retain the older “PCI-E 5.0” label. Match the delivered revision and cable kit rather than applying today’s description to an older unit or a differently named PCIE5 II model.

Its +12 V rating is separate from total output. Allocate motherboard and CPU connections first, then check both GPU paths and remaining rail requirements. Native 16-pin support is useful for a compatible future card, but is not a substitute for an additional legacy cable run.

When a third separate PCIe cable matters

Choose the Seasonic when the build needs its three separate PCIe cables and remains within the 850 W output and rail limits. A cable-count requirement is separate from a wattage requirement.

Its buying advantage is three separate legacy PCIe cables, each with one connector, rather than MSI’s two runs with paired ends. Choose it when a documented mixed-card configuration needs that third run while still fitting the complete 850 W budget.

Both units have a 140 mm PSU depth, so choosing Seasonic does not reduce PSU-body clearance. Nor does a Cybenetics Platinum efficiency designation establish a noise advantage or a particular saving at your workload.

Order the FOCUS GX-850 ATX 3.1 v4 represented by the listing and sources. The FOCUS name also covers older supplies and a newer v5 generation; do not transfer cable counts or certification details between them. Its three legacy feeds are insufficient for the four-feed 3090 example even before considering the wattage shortfall.

Higher-load pick: HX1500i, with the exact card map

For two reference-style 3090 power paths needing two PCIe 8-pin feeds per card, the current HX1500i kit provides enough separate runs. Reserve the required EPS connections for the CPU, allocate four approved PCIe cables to the GPU paths, and check the available sockets. Leave unused alternative cables out of the count.

NVIDIA’s reference 3090 uses an included adapter to its 12-pin connector. That is not the modern 16-pin 12V-2x6 connection. Use the approved card-specific adapter and every required input; do not try to substitute the newer native cable because the names look similar.

For partner cards needing three independent 8-pin feeds each, the requirement becomes six runs. None of these supplied kits establishes that arrangement. Do not buy the Corsair as a complete six-feed solution: resolve an explicitly supported kit or choose another documented PSU arrangement first.

Its input-voltage derating also matters. Follow the delivered label and manual; the table’s 1,500 W figure must not be assumed throughout the input range.

Keep efficiency, cabling and wall input separate

80 PLUS is CLEAResult’s efficiency program. Cybenetics is a separate certification scheme: this Seasonic is 80 PLUS Gold and Cybenetics Platinum, not “80 PLUS Platinum.” Keep the body attached to the tier when comparing badges. A ten-year warranty also does not establish an independent reliability ranking.

PSU output capacity is DC; a plug-in meter reads AC input. Do not subtract a badge percentage from capacity or use it as a constant conversion at every load. The power-meter guide covers choosing an appropriate measurement tool, while the monthly-cost guide keeps electricity use separate from component telemetry.

Check fit and the original cable kit before ordering

Map PSU sockets, independent cable runs and component ends separately. Seasonic’s high-power-card guidance recommends separate PCIe cables for the high-power cards it describes. Apply the exact PSU and board instructions; EPS and PCIe connections are different jobs.

Keep modular cables with the PSU models that explicitly support them. An old lead fitting a socket does not establish its pinout. Buy the complete approved kit, check cable lengths and GPU routing with the case closed, and follow the manufacturer’s seating and clearance instructions. Keep the PSU enclosure closed.

Our two-GPU build record documents its parts and GPU observations, not a validated PSU sizing test. Use it as context, not approval for another power supply. The quiet-cooling buying guide compares case fans and CPU coolers by mounting size, CPU clearance and supported specifications; it also explains how to test the assembled result.

Choose MSI for the two-single-input-card budget, Seasonic when the third separate PCIe cable is required, or HX1500i for the higher-load example with its input-voltage limits checked. Check your exact cards before ordering.

Once you have the wattage and cables sorted, choose a case for two GPUs. Its slot-spacing examples show when an eighth or ninth rear position helps, and the checklist leaves room for both coolers and power plugs.