PC Power Supplies

Every Power Supply Spec, Explained

A power supply does not make your PC faster. Every 850 W unit delivers 850 W, and a more expensive one will not add a single frame. What it decides is whether the machine is stable, how long it lasts, what it can plug into, and how much you can hear it. Here is what each spec in the table above actually does, how much it matters, and a steer on what is worth paying for.

Wattage

The continuous power the unit is rated to deliver. This is a threshold, not a scale: once a unit covers what your build draws, more watts do nothing for you. A larger unit does not run a small load badly, so the wattage filter here is a minimum rather than a bucket, and setting 850W keeps the 1000W units in the list. Importance: high, then irrelevant. Add up the graphics card and processor, allow headroom for the rest and for transient spikes, and buy the cheapest good unit that clears it. Spending the difference on a higher efficiency grade at the wattage you need beats buying capacity you will never use.

80 PLUS efficiency

How much wall power reaches your components instead of becoming heat. At half load, Bronze certifies about 85%, Gold about 90%, Platinum about 92% and Titanium about 94%. The electricity saving between grades is small on a machine that games in the evenings, a few dollars a year between Gold and Platinum. Importance: high, but not for the reason people think. Hitting a higher grade requires better components and a stronger internal design, so the badge is a reliable shorthand for build quality and for how much heat the unit dumps into your case. Gold is the sensible floor for a gaming build; go higher when the price gap is small rather than to save money.

ATX standard and the 12V-2x6 connector

The ATX12V specification version the unit was built to. ATX 3.0 and 3.1 require it to ride out power excursions far above its rating for microseconds, which is exactly what a modern graphics card produces. A unit built to the older spec can trip under a card that is comfortably inside its wattage, which reads as a random shutdown mid-game. The 12V-2x6 connector (the 16-pin cable, and the successor to 12VHPWR) carries up to 600 W down a single lead and is what current high-end cards expect. Importance: high on a modern build, low on an older one. If your card ships with a 16-pin adapter, filter for a unit that has the connector natively and skip the adapter entirely.

Form factor: ATX, SFX and SFX-L

The physical standard, and it is decided by your case rather than by preference. ATX is full size at 150 × 86 mm. SFX is the small-form-factor standard at 125 × 63.5 × 100 mm, and SFX-L is the same but 130 mm deep, which is what makes room for a 120 mm fan instead of an 80 or 92. A smaller unit fits a larger bay with an adapter bracket; a larger one will not fit a smaller bay at any price. Importance: absolute, but binary. Check what your case takes, then treat it as a filter and forget it. Size earns no points in our score, because an SFX unit is not a worse power supply, it is a different compatibility decision. ATX vs SFX covers the trade in detail.

Depth and case clearance

Width and height are fixed by the standard, so depth is the dimension that actually decides whether a unit fits. ATX units run from about 140 mm to 220 mm, and your case publishes a maximum. The case-clearance filter here matches on that measurement, and it deliberately hides any unit whose depth is not published, because telling you something fits when the figure is unknown is worse than leaving it out. Importance: high in a compact build, low in a full tower. Deeper units also leave less room for cable routing in front of them, which is the part people discover during the build rather than before it.

Modularity

Whether the cables detach. Fully modular means every cable does, so you attach only the ones your build uses. Semi-modular fixes the motherboard and CPU leads and detaches the rest. Non-modular has them all permanently attached, and the ones you do not need have to be hidden somewhere inside the case. Electrically the three are identical. Importance: medium in a small or glass-fronted case, low in a roomy one. It is a convenience feature you are buying, not a performance one. One hard rule: never reuse cables between different power supplies, even from the same brand, because the pinouts are not standardised and doing so can destroy parts.

Connectors: PCIe, EPS, SATA and Molex

What you can actually plug in. PCIe 6+2 leads power the graphics card, and a card wanting three eight-pin connectors needs a unit that supplies three. EPS (also written 4+4 or 8-pin CPU) powers the processor, and most modern boards want one, with high-end boards taking two. SATA leads run drives and fan hubs, and Molex is the older four-pin still used by some fan controllers and pumps. Importance: high, and easy to get wrong. Count what your specific card and board ask for before you buy, since a unit with plenty of watts can still be short a cable. A dash in these columns means the manufacturer does not publish the figure, which is not the same as zero.

Measured noise

A letter grade from the Cybenetics lab, which tests units in an anechoic chamber across the full load range and publishes a result from A++ down. This is a measurement, not a manufacturer claim, and it is the single most useful number in the table for anyone who sits near their machine. Importance: high, and almost never published. A grade only exists for units the lab has tested, so a dash means untested rather than loud, and filtering on noise hides those units rather than ranking them badly. Note that a semi-fanless unit is silent at idle whatever its grade, because the fan does not spin until the load crosses a threshold.

Fan size

Bigger fans move the same air more slowly, and slower is quieter. ATX units usually carry a 120 or 140 mm fan, SFX-L a 120 mm, and SFX an 80 or 92 mm. Importance: low on its own. It is a decent proxy where no measured grade exists, but a well-designed unit with a smaller fan beats a poorly designed one with a larger fan, so prefer the measured noise grade whenever there is one.

Warranty

How long the manufacturer will replace it, which is their own financial bet on the unit surviving. Budget units run three to five years, strong ones seven to ten, and the best twelve. Importance: high as a signal. A power supply is the one component that can take other parts with it when it fails, and it is the component people keep across two or three builds. Nobody underwrites a decade on a unit they expect to come back.

Platform, topology and who builds it

Most brands do not manufacture their own units. The platform is the actual design inside, built by a company such as Seasonic, CWT, FSP or HEC, and the same platform often appears under several badges. Two terms matter: LLC resonant topology is the modern efficient approach, and DC-DC minor-rail regulation is the modern way to hold the 5V and 3.3V rails steady. The alternative, group regulation, is the real quality cliff: load one rail hard and another drifts out of specification. Importance: medium, and a strong tiebreak. Between two units at the same price and grade, the one on the better platform is the better unit, and this is the layer that separates them.

Protections

The circuits that shut the unit down instead of letting it damage something: over-voltage, under-voltage, over-current, over-power, over-temperature and short-circuit protection. Importance: high, and close to non-negotiable. Any reputable unit carries the full set, so this is less a feature to shop for than a box to check before buying something unfamiliar. A unit that does not publish its protections at all is telling you something.

Quality score and value

Our own 0–100 index, built from six of the specs above: the efficiency grade, the ATX standard crossed with 12V-2x6 support, measured noise, warranty length, the internal platform and modularity. Better always scores higher, but the steps are uneven on purpose: Bronze to Gold is worth 11 of the 25 efficiency points, Gold to Titanium only 6. Value is that score divided by the current price, which is what the table sorts by out of the box. Importance: read it with the confidence bar. A factor we hold no value for scores zero rather than being skipped, so a unit we know almost nothing about can never outrank a fully specified one. The small bar beside each score shows how much of it we actually measured, and a low score on a low bar means unverified rather than bad.

Price per watt

The current price divided by the rating. It is the quickest way to spot a unit that is expensive for what it delivers, and the fairest way to compare two units at different wattages. Importance: a sanity check, not a ranking. It says nothing about efficiency, noise, warranty or build quality, so a budget unit will usually look best on it. The useful move is to filter to the size, grade and connectors you need first, then sort by price per watt inside that set, which answers “what is the cheapest unit that meets my requirements”.

Put together, the approach is simple: work out the wattage, filter to the form factor your case takes, set the efficiency grade and the connectors your graphics card needs, then sort by value and take the highest-scoring unit you can see the evidence for. Everything you save is better spent on the graphics card or the processor, where it actually buys frames.