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Rectangular ATX power supply in matte black finish with fixed cables and a 120 mm fan grille

Seasonic

Seasonic S12III-550GB 550W 80+ Bronze power supply

SKU CH-FWJ4-YEQ72 MPN S12III-550GB

Delivers 550 W of 80 PLUS Bronze certified power with a single +12 V rail, two 6+2-pin PCIe connectors, six SATA connectors, a 120 mm sleeve-bearing fan under smart silent control, active PFC.

  • Max wattage550 W
  • Modular cablingNon-Modular
  • Fan configuration120 mm Sleeve Bearing fan
  • Power factor correctionActive
  • Main power connector20+4Pin
  • 12V railsSingle

Model ATX 80+ Bronze (550W)

  • Delivers 550 W continuous power for stable system operation
  • 80 PLUS Bronze certification reaches 85 % efficiency at 50 % load
  • Single +12 V rail with 45 A simplifies high-demand GPU builds
  • 120 mm fan with S2FC adjusts speed for quiet cooling
  • Japanese capacitors rated at 105 °C ensure long-term reliability

Power for mainstream and gaming builds

This Seasonic S12III Bronze Series unit delivers 550 W of continuous power for a mainstream system or gaming rig. It meets the 80 PLUS Bronze standard with 82% efficiency at 20% and 100% load and 85% at 50% load. A single +12 V rail simplifies power distribution to the CPU and graphics card. Japanese capacitors rated at 105 °C support long-term reliability.

Fixed cables and a 140 mm depth

The non-modular design provides every cable needed for a standard PC, including a 20+4-pin main connector, two 6+2-pin PCI-Express connectors and six SATA power connectors. At 140 mm long the unit fits most ATX cases, but verify clearance before ordering. The 120 mm sleeve bearing fan is regulated by Seasonic S2FC fan control to balance noise and cooling.

550 W on a single +12 V rail

The single +12 V rail design delivers the full 550 W to CPU and GPU without multi-rail balancing. Active PFC accepts 110-240 V input at 50/60 Hz for worldwide use. Protection circuits include OPP, OVP, UVP and SCP to safeguard components. MTBF exceeds 100,000 hours.

How it compares

Measured against everything we stock in ATX Desktop Power Supplies, at today’s prices. Recalculated every night.

Price $52.99
Cheaper than about 90% of the 10,869 comparable items (median $142.99).
Max wattage 550 W
Lower than about 82% of the 930 comparable items (median 850 W).

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Specifications

Product
Brand nameSeaSonic
Product lineS12III Bronze Series
Model nameS12III-550 GB (SSR-550GB3)
Product typeIntel ATX 12 V
Ports & slots
PCIe power connectors2 × 6+2-Pin
SATA power connectors6
Output type+3.3 V@20A, +5 V@20A
Connection types1 x Main Power (24/20 pins)
1 x CPU (8/4 pins)
2 x PCIe (8/6 pins)
6 x SATA
3 x Peripheral
1 x Floppy
Power
Max wattage550 W
Modular cablingNon-Modular
Power factor correctionActive
Main power connector20+4Pin
12V railsSingle
Efficiency certification80 PLUS BRONZE Certified
Overvoltage protectionYes
Supply voltage110–240 V
AC input frequency50/60 Hz
Rated input current8–4 A
Size & build
Product dimensions3.39 in × 5.51 in × 5.91 in
Shipping weight2.16 kg
Package size267 × 201 × 99 mm
Compatibility
PSU length limit140 mm
Environment & compliance
Regulatory approvalsSafety and EMC: cTUVus, TUV, Gost-R, UkrTEST, CB, BSMI, Semko, CCC, CE, FCC, C-tick
Environmental Compliance: Energy Star, RoHS, WEEE, REACH
More details
Fan configuration120 mm Sleeve Bearing fan
Mean time between failures>100,000 h

Other versions of this model

1 more in the same range

Questions about this item

Will this unit fit in a standard ATX case with limited depth?

The chassis is 140 mm long, which matches the typical ATX power-supply clearance in most mid-tower cases.

Can it power a modern graphics card that needs two PCIe power plugs?

It includes two 6+2-pin PCIe connectors, so a card requiring up to two 8-pin plugs can be connected directly.

What efficiency can I expect at typical gaming loads?

The 80 PLUS Bronze rating guarantees 85 % efficiency at 50 % load and 82 % at both 20 % and 100 % load.

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