ATX vs SFX PC Power Supplies in 2026: Key Differences
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Choosing between an ATX vs SFX PC power supply depends on your case size and build goals. Both the MSI MAG 850W and SilverStone 700W offer 80 Plus Gold efficiency and fully modular cables for clean builds. The main difference is physical size. ATX units fit standard mid-towers, while SFX units are for compact cases. You need to match the form factor to your chassis to ensure proper fit and airflow.
Key differences
| Aspect | MSI MAG 850W Fully Modular ATX Power Supply | SilverStone 700W SFX 80 Plus Gold Power Supply |
|---|---|---|
| Form Factor | ATX | SFX |
| Wattage | 850W | 700W |
| ATX Version | ATX 3.1 | not listed |
| PCIe Version | PCIe 5.1 | not listed |
| Dimensions | 8.75 x 4.92 x 12 inches | 3.94 x 2.5 x 4.92 inches |
Which one should you choose?
Choose MSI MAG 850W Fully Modular ATX Power Supply if
- You are building in a standard mid-tower or full-tower case.
- You need higher wattage for demanding gaming or workstation tasks.
- You want the latest ATX 3.1 and PCIe 5.1 connectivity standards.
Choose SilverStone 700W SFX 80 Plus Gold Power Supply if
- You are building in a small form factor (SFF) case.
- You prioritize compact dimensions and lower weight.
- You need a standard SFX mounting footprint.
Verdict: The MSI MAG 850W suits standard builds requiring high power and modern connectivity. The SilverStone 700W is the right choice for compact cases where space is limited. Your decision rests on whether your case accepts ATX or SFX units.
ATX vs SFX PSU Comparison
form factor
The MSI MAG is an ATX unit, measuring 12 inches long, 4.92 inches high, and 8.75 inches wide. This is the standard size for most mid-tower and full-tower cases. The SilverStone is an SFX unit, measuring 4.92 inches long, 2.5 inches high, and 3.94 inches wide. SFX units are designed for small form factor builds. The SilverStone fits in tight spaces where an ATX unit will not. You must check your case compatibility first. The MSI requires more internal volume. The SilverStone is the only choice for compact cases.
wattage
Power output differs significantly between these two models. The MSI MAG provides 850W of continuous power. This higher output supports high-end graphics cards and overclocked CPUs. The SilverStone provides 700W of continuous power. This is sufficient for mid-range gaming systems but may limit extreme builds. If your system requires more than 700W, the SilverStone cannot support it. The MSI offers more headroom for future upgrades. You should match the wattage to your component power draw.
atx version
The MSI MAG supports the ATX 3.1 specification. This newer standard includes specific requirements for modern power delivery and transient response. The SilverStone data does not list an ATX version. It likely follows an older or unspecified standard. ATX 3.1 readiness ensures compatibility with the latest motherboard power connectors and protocols. If you are building a new high-end system, the ATX 3.1 standard is preferable. The MSI is the only unit with this explicitly stated version support.
pcie version
Graphics card power connections have evolved. The MSI MAG supports PCIe 5.1 and includes a 12V-2x6 connector. This is the native connector for modern high-end GPUs like the RTX 40 series. The SilverStone data does not list PCIe version support or specific connector types. You may need adapters for newer cards if the SilverStone lacks native support. The MSI connects directly to PCIe 5.1 compatible graphics cards without extra cables. This reduces clutter and potential connection issues.
efficiency rating
Both units share the same efficiency certification. The MSI MAG is 80 Plus Gold certified. The SilverStone is also 80 Plus Gold certified. This means both convert at least 87% of AC power to DC power at typical loads. You will save similar amounts of electricity with either unit. Neither unit has a higher efficiency rating in the data. The SilverStone mentions strict voltage regulation and low ripple, which supports stable power delivery. The efficiency outcome is identical for your energy bills.
modularity
Cable management affects airflow and aesthetics. The MSI MAG is fully modular. You only connect the cables your system needs. The SilverStone is also fully modular. It uses flexible flat arrays for its cables, which can make routing easier in small cases. Both units allow you to remove unused cables. This reduces internal clutter in both ATX and SFX builds. The modularity level is equal. The SilverStone cable style may offer a slight practical advantage in tight spaces, but both are fully modular.
Which PSU fits your build needs
Small form factor builders
You need a compact unit for tight cases. The SilverStone SFX measures just 4.92 by 3.94 inches. It fits where ATX units cannot. The 700W output supports most standard components. Its 92mm fan ensures quiet operation at 18 dBA. This size compatibility is the primary advantage for mini-ITX or micro-ATX builds.
High performance gaming rigs
You require maximum power for modern GPUs. The MSI MAG provides 850W of continuous output. It meets ATX 3.1 and PCIe 5.1 standards. The included 12V-2x6 connector supports next-generation graphics cards directly. The larger ATX form factor allows for better airflow and thermal management under heavy loads.
Users seeking long term warranty
You want extended protection for your investment. The MSI MAG offers a 10-year warranty. This coverage is longer than typical industry standards. The SilverStone unit does not list a specific warranty duration in the provided data. A longer warranty period provides greater peace of mind for expensive components.
Quick picks
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | MSI MAG 850W Fully Modular ATX Power Supply | Standard ATX gaming builds with modern GPUs | Check price of MSI MAG 850W Fully Modular ATX Power Supply on Amazon |
| 2 | SilverStone 700W SFX 80 Plus Gold Power Supply | Small form factor builds needing 700W | Check price of SilverStone 700W SFX 80 Plus Gold Power Supply on Amazon |
The products compared
MSI MAG 850W Fully Modular ATX Power Supply
Best for: Standard ATX gaming builds with modern GPUs
- Wattage
- 850W
- Efficiency Rating
- 80+ Gold
- Modularity
- Fully Modular
- ATX Version
- ATX 3.1
- PCIe Connector Type
- 12V-2x6
- Warranty
- 10 Year
View on Amazon: MSI MAG 850W Fully Modular ATX Power Supply Affiliate link
This is an 850W ATX power supply designed for modern gaming builds. It carries an 80 Plus Gold efficiency rating and supports the latest ATX 3.1 and PCIe 5.1 standards. The unit is fully modular and uses a single 12V-2x6 connector for graphics cards. It measures 8.75 by 4.92 by 12 inches. This model suits users building high-end PCs who need reliable power delivery and modern connector compatibility.
Pros
- 850W output capacity for high-end components
- 80 Plus Gold efficiency rating
- ATX 3.1 and PCIe 5.1 ready
- Fully modular cable design
- 12V-2x6 connector for modern GPUs
Cons
- Standard ATX size may not fit small form factor cases
- No mention of fan noise levels or zero-RPM mode
- 10-year warranty is standard, not the longest available
Good fit if
- You are building a standard ATX mid-tower or full-tower case
- You need a single 12V-2x6 connector for your graphics card
- You want 80 Plus Gold efficiency for better power usage
Skip if
- You are building in a small form factor case requiring SFX
- You need a higher wattage than 850W
- You prefer a fully silent operation with no fan curve data
Verdict: MSI MAG A850GL 850W ATX provides solid power and modern connectivity for standard desktop builds. It is a reliable choice for gamers using current-generation graphics cards in standard-sized cases.
SilverStone 700W SFX 80 Plus Gold Power Supply
Best for: Small form factor builds needing 700W
- Form Factor
- SFX (what this guide is about)
- Wattage
- 700W
- Efficiency Rating
- 80 PLUS Gold
- Modularity
- Fully Modular
- Fan Size
- 92mm
- Dimensions
- 4.92 × 3.94 × 2.5 inches
View on Amazon: SilverStone 700W SFX 80 Plus Gold Power Supply Affiliate link
This SilverStone power supply uses the compact SFX form factor, fitting into smaller cases where standard ATX units do not. It delivers 700W of power with 80 PLUS Gold efficiency. The fully modular design allows you to connect only the cables you need. A 92mm fan keeps noise levels low at 18 dBA. It features all Japanese capacitors for stable voltage regulation.
Pros
- 80 PLUS Gold efficiency rating
- 700W power output
- Fully modular cable design
- Quiet 92mm FDB fan
Cons
- SFX form factor not compatible with ATX mounting holes
- Heavier at 3.09 pounds
- Smaller 92mm fan may run louder under heavy load
Good fit if
- You need a compact power supply for a small form factor case
- You want high efficiency with 80 PLUS Gold certification
- You prefer fully modular cables for cleaner builds
Skip if
- You require an ATX form factor for standard cases
- You need more than 700W of power
- You want a larger 120mm or 140mm fan for passive cooling
Verdict: SilverStone 700W SFX Gold PSU is a solid choice for builders using small cases who need reliable 700W power. It suits those prioritizing efficiency and cable management over raw wattage.
Specifications side by side
| Spec | MSI MAG 850W Fully Modular ATX Power Supply | SilverStone 700W SFX 80 Plus Gold Power Supply |
|---|---|---|
| Wattage | 850W | 700W |
| Efficiency Rating | 80+ Gold | 80 PLUS Gold |
| Modularity | Fully Modular | Fully Modular |
| ATX Version | ATX 3.1 | not stated |
| PCIe Connector Type | 12V-2x6 | not stated |
| Fan Size | not stated | 92mm |
| Warranty | 10 Year | not stated |
| Form Factor | Compact | SFX |
| PCIe Version | PCIe 5.1 | not stated |
| Recommended Use | Gaming | not stated |
| Connector | 12V-2x6 Connector | not stated |
| Dimensions | 12 × 8.75 × 4.92 inches | 4.92 × 3.94 × 2.5 inches |
| Weight | not stated | 3.09 pounds |
| Size | 850W (PCIE 5) | 700W |
| Color | not stated | Black?Lead-Free Paint? |
| Model | not stated | SST-SX700-G |
Frequently asked questions
Can an ATX power supply fit in a small form factor case?
No, an ATX power supply will not fit in a small form factor case. The MSI MAG ATX unit measures 12 inches long, which exceeds the space available in compact chassis. You must choose an SFX unit, like the SilverStone 700W, which is only 4.92 inches long. This size difference is the primary constraint for mini-ITX builds.
Is an SFX power supply less efficient than an ATX one?
No, efficiency ratings are independent of physical form factor. Both the MSI MAG ATX and SilverStone SFX models in this comparison hold 80 Plus Gold certifications. This means both units convert electrical energy with high efficiency during operation. You can expect similar power loss characteristics regardless of whether you select the larger ATX or smaller SFX variant.
Do I need a fully modular power supply for my build?
You do not strictly need one, but it significantly improves cable management. Both the MSI MAG and SilverStone units featured here are fully modular. This allows you to connect only the cables your components require, reducing clutter inside the case. This is especially helpful in tight SFX builds where airflow and space are limited.
Which power supply is better for modern graphics cards?
The MSI MAG ATX is better for modern high-end graphics cards. It supports ATX 3.1 and PCIe 5.1 standards, featuring a native 12V-2x6 connector. This direct connectivity simplifies power delivery for the latest GPUs. The SilverStone SFX lacks these specific modern interface details in its listed specifications, making the ATX option more future-proof for top-tier hardware.
How much wattage can an SFX power supply provide?
SFX power supplies can provide substantial wattage, though often less than ATX equivalents. The SilverStone SFX model shown delivers 700W, which supports most standard components in small builds. While ATX units like the MSI MAG can reach 850W, the SFX form factor still offers enough power for many compact gaming and workstation configurations without sacrificing efficiency.
What is the physical size difference between ATX and SFX?
The size difference is significant, affecting case compatibility. The MSI MAG ATX measures 12 by 8.75 by 4.92 inches. The SilverStone SFX is much smaller at 4.92 by 3.94 by 2.5 inches. This compact footprint allows the SFX unit to fit into cases where the larger ATX unit simply cannot physically install.