Given the number of massive CPU coolers and loud graphics cards that make their way through our lab, it's easy to overlook the noise coming from power supplies. In general, power supply fans are drowned out by other system components. Even a mechanical hard drive tends to be more noticeable than a nice, big 120 mm cooler lackadaisically blowing air through large vents in a PSU.
But just ask anyone who's been burnt by a cheap power supply, or someone who hasn't blown out their chassis in a couple of years: PSU fans can get really loud.
What if you simply want a super-quiet machine? A computer for the living room or bedroom, perhaps. There are such things as passively-cooled graphics cards. Even more effective, liquid cooling has the potential to draw heat away from your components and dissipate it using larger, slower-spinning fans that generate barely a whisper. Swap out that clacking hard drive for an SSD and really, there's not much left inside your PC to disrupt the glorious silence.
Well, almost. There's still the issue of that ever-turning power supply fan.
Today's energy-efficient power supplies waste less power as heat than they used to. However, they still require cooling. And of course, the easiest way to achieve that is with a fan. But there are passively-cooled power supplies without fans (and other models specifically equipped with low-noise fans) for applications that demand silence.
We grabbed three PSUs purportedly known for their acoustic qualities, hoping to find at least one worth recommending. Upon hearing our call for submissions, Seasonic and SilverStone each sent in a fanless model to test. The former gave us a look at its X-460, while the latter shipped off its SST-ST50NF. For the purposes of comparison, we grabbed a single fan-cooled unit that's supposed to be ultra quiet: be quiet!'s Straight Power E9 CM 480 W. Unfortunately, you can't get it in the U.S., so it's really serving as a point of reference here today.
It's also notable that none of these are designed to sustain more than 500 W of output. Higher-wattage power supplies generate more heat under load, even if they're very efficient. As a result, passive cooling generally isn't an option once you start looking at more enthusiast-oriented configurations.
Our German team tested be quiet's Straight Power E9 CM 580 W in a previous round-up. That's this unit's bigger brother. The company claims that they're both the quietest models it sells. Although you can't buy the Straight Power here in the U.S., we're using it as a control, since its 480 W rating sits right between Seasonic's 460 W and SilverStone's 500 W specifications.
As far as specs go, be quiet's 480 W offering is only slightly different from its 580 W effort. It employs four +12 V rails, each supplying up to 18 A, and a modular cabling system with long, sleeved power cords. The number of receptacles on the power supply is more than ample for the systems a 480 W PSU might drive. In fact, it includes enough connectors for up to two graphics cards in SLI or CrossFire.
| be quiet! Straight Power E9 CM 480 W | ||||||||
|---|---|---|---|---|---|---|---|---|
| AC Input | 100-240 V, 50-60 Hz | |||||||
| DC Output | +3.3 V | +5 V | +12 V (#1) | +12 V (#2) | +12 V (#3) | +12 V (#4) | -12 V | +5 Vsb |
| 24 A | 22 A | 18 A | 18 A | 18 A | 18 A | 0.3 A | 3.0 A | |
| Individual Output | 15 W | 3.6 W | ||||||
| Rail Utilization | Sys | Sys | CPU And VGA | |||||
| Combined Output | 130 W | 456 W | ||||||
| Total Continuous Output | 480 W | |||||||
| Peak Output | 550 W | |||||||
Efficiency, According to the 80 PLUS Specification


Efficiency Across the Power Spectrum


In the test lab, the 480 W power supply follows and then surpasses the performance of the 580 W model. It conforms to the 80 PLUS spec even more closely, sporting particularly high efficiency at low loads. At 25 W, for example, the 480 W PSU comes close to 80% efficiency, which is a respectable number that ranks among the best performances we've seen. In standby, it only draws 0.18 W.
Our lab tests show that be quiet!'s E9 CM 480 W doesn't encounter any regulation issues, and also achieving low low ripple and noise values on the DC rails.
Last but not least, even when you're in a quiet room the Straight Power E9's fan can only really be heard close to the power supply itself.
A Peek at the PCB
The 480 W PSU's interior looks a lot like the 580 W model we've already reviewed. All be quiet! power supplies are manufactured by FSP and are similar to that company's Aurum family. Taiwanese firm CapXon makes the Straight Power E9's capacitors. Although they're not the premium caps from Japan, which FSP uses in its own-branded power supplies, they're still decent and shouldn't cause problems.
We did notice an extra ceramic capacitor in the mains-side circuit. Its task is to eliminate the chirping sound that sometimes emanates from power supplies. Another design feature intended to help reduce noise is a fan mount sitting on rubber grommets. This prevents vibrations from being amplified by the power supply enclosure. The manufacturing and soldering quality are both impeccable. Our only complaint is that FSP does not use heat shrink tubes to cover the locations where cables are soldered onto the PCB.
The be quiet! Straight Power E9 CM 480 W is very quiet and boasts an 80 PLUS Gold rating. It demonstrates no apparent weakness in our testing, and offers high efficiency across the entire load spectrum. Its feature set and quality are top notch, and although it is actively cooled, this power supply is the next best thing to fanless. Unfortunately, it isn't available to our U.S. audience, and only stands in as a comparison point for our other two passively-cooled contenders.
Seasonic's X-460 is also adorned with the coveted 80 PLUS Gold logo. Rated for 460 W, the X-460 comes close to the be quiet! unit's output. However, Seasonic does this without employing active cooling (a fact that is advertised in several places on the packaging).
The box also contains a leaflet that explains the peculiarities of a fanless supply.
The X-460's feature set is typical for the $100+ price range. You get two PCIe connectors, as well as five SATA and five four-pin Molex connectors. Seasonic's X-series features fully modular cable management, which sets it apart from much of its competition. The cable lengths are sufficient, though they're a bit shorter than what you get from the other two power supplies in this round-up. The X-460 employs a single +12 V rail able to deliver up to 38 A.
| Seasonic X-460 | ||||||||
|---|---|---|---|---|---|---|---|---|
| AC Input | 100-240 V, 50-60 Hz | |||||||
| DC Output | +3.3 V | +5 V | +12 V (#1) | +12 V (#3) | +12 V (#3) | +12 V (#4) | -12 V | +5 Vsb |
| 20 A | 20 A | 38 A | 0.5 A | 2.5 A | ||||
| Individual Output | 6 W | 12.5 W | ||||||
| Rail Utilization | Sys | Sys | CPU And VGA | |||||
| Combined Output | 100 W | 456 W | ||||||
| Total Continuous Output | 460 W | |||||||
| Peak Output | n/a | |||||||
Efficiency, According to the 80 PLUS Specification


Efficiency Across the Power Spectrum


Seasonic's X-460 is not the first model in the company's X-series that we've reviewed. As with the previously-tested models, everything we encountered we liked. The power supply exceeds all of the 80 PLUS Gold requirements. Even subjected to low loads, its efficiency is quite good (though it falls short of be quiet!'s Straight Power E9 CM 480 W).
The X-460’s ripple and noise results are among the best we have ever seen. In all other disciplines, this Seasonic unit performs as expected, just like a good power supply should.
Before discussing our thermal measurements, we want to describe how we take temperatures from a fanless supply. Because there is no active cooler, there is no exhaust air. Thus, we take our results close to, but not in contact with, the top of the power supply enclosure. With an ambient air temperature of 64 degrees Fahrenheit, the temperature near the X-460 was 118 degrees Fahrenheit. That's a difference of 54 degrees.
A Peek at the PCB
We expected the interior of a fanless power supply to be crammed with heat sinks. But the Seasonic X-460’s interior is not overloaded with heat sinks at all. Yes, there are more than you'd find in an actively-cooled model, and the MOSFETs in particular are bolted to massive aluminum blocks. Overall, the interior looks organized and neat. The fact that there are almost no wires soldered into the PCB makes it appear even neater. And as we've come to expect from Seasonic, the soldering quality is very good.
Seasonic uses premium brand components from Japan. All electrolytic capacitors are sourced from Nippon Chemikon; most of them are polymer aluminum. The MOSFETs are premium Infineon models. No corners are cut in the electronic circuitry. The input filter circuitry is top-notch, and heat shrink tubes protect what would otherwise be bare cabling. Overall, the manufacturing quality is impeccable.
Fanless at its best. We can’t think of any other phrase that so succinctly and accurately summarizes our impression of the Seasonic X-460. The power supply sports excellent efficiency, performs reliably and accurately, and it is also perfectly silent. A peek inside shows its high manufacturing quality. Taking all of this into account, we think the street price of $130 is reasonable indeed.
At first glance, SilverStone's SST-ST50NF looks like a gigantic heat sink. Basically, that’s what it is. The top consists of aluminum cooling fins. And its hefty weight, close to eight pounds, offers some indication of this power supply's purpose: achieve maximum cooling performance without a fan. In other words, the SilverStone SST-ST50NF (called the Nightjar after the nocturnal bird) is a fanless power supply like Seasonic's X-460. Unlike the X-460, though, Silverstone's offering is only 80 PLUS Bronze-certified, leading us to assume that it'll dissipate more heat as a result of lower efficiency. This explains why SilverStone turns its entire enclosure into a giant heat sink...at considerable expense, we're guessing.
Unsurprisingly, the 80 PLUS Bronze-certified SilverStone power supply's liberal use of aluminum makes it cost significantly more than Seasonic's X-460. It's as much as $70 more when you compare the lowest prices for each online, taking the SilverStone unit's total to $200.
For that price, you get the highest total wattage of the three power supply's we're comparing. But note that its +12 V rail is limited to the same 38 A current as Seasonic's offering. And, in spite of a hefty price, the SST-ST50NF doesn't employ modular cabling. All of its leads are soldered directly to the PCB. Some folks consider this good (one less failure point) and others prefer modular connectors for their benefit to cable management. The cables are sleeved at least, though they're are too short by several inches. This detracts from an otherwise attractive-looking unit. Fortunately, you get plenty of cables and connectors.
The SilverStone PSU's specs are almost identical to the Seasonic unit's, both armed with a single 38 A, +12 V rail multiplying out to 456 W. SilverStone sets itself apart with a total continuous output of 500 W, whereas Seasonic is only rated for 460 W.
| SilverStone SST-ST50NF | ||||||||
|---|---|---|---|---|---|---|---|---|
| AC Input | 110-240 V, 50-60 Hz | |||||||
| DC Output | +3.3 V | +5 V | +12 V (#1) | +12 V (#3) | +12 V (#3) | +12 V (#4) | -12 V | +5 Vsb |
| 18 A | 18 A | 38 A | 0.5 A | 2.5 A | ||||
| Individual Output | 32 A | 6 W | 12.5 W | |||||
| Rail Utilization | Sys | Sys | CPU And VGA | |||||
| Combined Output | 120 W | 456 W | ||||||
| Total Continuous Output | 500 W | |||||||
| Peak Output | 550 W | |||||||
Efficiency, According to the 80 PLUS Specification


Efficiency Across the Power Spectrum


The 80 PLUS Bronze efficiency requirements aren't as stringent. So, while the SST-ST50NF does meet the organization's Bronze-level requirements, its efficiency value at low loads is far worse than the values recorded from the other two contenders. At 25 W, its efficiency is only 60%. With that said, it behaves like a typical Bronze-certified power supply, and does not stand out negatively among other Bronze-level supplies.
Unfortunately, the same cannot be said about the ripple voltage on its +12 V rail. At 129 mV, it does not even comply with ATX standards.
On the positive side, the SST-ST50NF sports an above-average hold-up time of more than 40 ms. The Nightjar power supply passes all other tests with flying colors. We measured a temperature increase of 49 degrees Fahrenheit, which is slightly less than the temperature increase of the Seasonic supply. Also, we're fans of the warning LED on the back of the power supply that warns of critical internal temperatures (though we're not sure you'd see it light up behind your PC).
A Peek at the PCB
The first thing we noticed after opening SilverStone's SST-ST50NF was its massive heat sinks covering large parts of the circuit board. This is a stark contrast to the Seasonic X-460.
Obviously, the dramatically larger heat sinks are necessary in light of the Nightjar's lower efficiency rating. At an identical load, it'll dissipate more heat than the 80 PLUS Gold-certified Seasonic unit. We can also see that the SilverStone supply has a well-designed input filter, unlike some low-cost solutions. SilverStone also uses premium-grade components, like Chemi-Con capacitors from Japan and Infineon MOSFETs. Instead of a single high-capacitance capacitor on the primary circuit, four smaller ones are used in parallel, which increases the surface area and thus aids in cooling. Copper shims between the power transistors and the large heat sink also serve to improve cooling.
The manufacturing quality of this fanless supply is impeccable, and the quality of the electronic parts is top-notch as well. However, the out-of-tolerance ripple voltage does raise questions about the electrical quality of this power supply. When we factor in the lower price and higher efficiency of competing models, like Seasonic's X-460, we find it difficult to recommend the fanless solution from SilverStone.
| Test Hardware | |
|---|---|
| AC Source | Chroma Programmable AC Source 6530 |
| Power Meter | Yokogawa WT210 Digital Power Meter |
| Loads | 4 x 600 W Chroma 63306 for 12 V testing 4 x 300 W Chroma 63303 for 5 and 3.3 V testing using Chroma HighSpeed- DC Load Mainframes 6334 |
| Oscilloscope | Tektronix DPO3034 Digital Phosphor Oscilloscope (300 MHz) |
| Test Procedure | |
| Voltages | 110 and 230 V |
| Standby Power | 0.25 A fixed current to simulate PC standby power on 5 Vsb |
| 80 PLUS Efficiency Testing | 100/50/20% load, relative to specified total output Load distribution across 12/5/3.3 V rails at the same proportion as specified for 100% testing at 110 V according to ATX 2.3 specification |
| Efficiency at Fixed Loads | 25, 50, 85, 300, 500 W loads Load distribution across 12/5/3.3 V rails at the same proportion as specified for 100% |
| Peak Load Test | 110% Overload Testing at maximum combined 12 V |
| Temperature Test | Air intake vs. Outtake temperature delta tracking highest delta during all tests |
For more test data about these three and other power supplies, please refer to our power supply charts.
Hold-Up Time, Inrush Current, Peak Load Test, and Short Circuit Protection Test



| Short Circuit Protection Test at 12 V | |
|---|---|
| Power Supply / Mains Voltage | Test Passed |
| Seasonic X-460 (115 V) | Yes |
| Seasonic X-460 (230 V) | Yes |
| be quiet! Straight Power E9 CM 480 W (115 V) | Yes |
| be quiet! Straight Power E9 CM 480 W (230 V) | Yes |
| SilverStone SST-ST50NF (115 V) | Yes |
| SilverStone SST-ST50NF (230 V) | Yes |
For more test data about these three and other power supplies, please refer to our power supply charts.



Standby Power and Temperature Measurements



For more test data about these three and other power supplies, please refer to our power supply charts.





Buy an actively-cooled power supply designed with low-noise in mind, or choose a fanless model. The choices are nearly the same, unless your hearing is acute. Of course, you could argue that if PSUs like the ones from Seasonic and SilverStone deliver high-quality DC power, just like the solutions with fans, why not go all-passive and cut the noise altogether?
Although it is true that the fanless power supplies from Seasonic and SilverStone are perfectly silent and ran in our test lab for extended periods of time, they did heat up about 50 degrees Fahrenheit above the ambient temperature. In an air-conditioned room, that shouldn't be a problem.
However, if you're in a room that gets beat-up by the sun all day or lacks A/C entirely, the thermal situation can get somewhat dicey, and a fanless power supply may very well hit its design limits. In that case, it's better to have a fan blowing through your power supply than to suffer the instability of an overheated component. It's worth noting that a PSU with a fan typically costs less than one without, due to the necessary measures to keep the passive unit cool enough.
But if you insist on absolute silence for your next build, Seasonic's X-460 rises to the top of our recommendation list. Its workmanship is excellent, and its price/performance ratio is quite good.
| Manufacturer | be quiet! | Seasonic | SilverStone |
|---|---|---|---|
| Model Name and Number | be quiet! Straight Power E9 CM 480 W | X-460FL | SST-ST50NF |
| Street Price | Not available in U.S. | $130 | $200 |
| Power Certification | 80 PLUS Gold | 80 PLUS Gold | 80 PLUS Bronze |
| Dimensions (WxDxH) | 150 x 180 x 86 mm | 150 x 160 x 86 mm | 150 x 160 x 86 mm |
| Weight | 2.6 kg | 2.77 kg | 3.5 kg |
| Operating Temperature | up to 40 °C | 0°C–50°C | 0°C–45°C |
| Warranty | Five Years | Five Years | Three Years |
| Power Specifications | |||
| Specification | ATX12V v2.31 | ATX12V v2.3 | ATX12V v2.3 |
| Specified Output Power | 480 W | 460 W | 500 W |
| Max. Peak Output | 550 W | n/a | 550 W |
| AC Input | 100 - 240 V | 100 - 240 V | 110 - 240 V |
| AC Voltage Selection | Auto voltage | Auto voltage | Auto voltage |
| DC Output +3.3V | 24 A | 20 A | 18 A |
| DC Output +5V | 22 A | 20 A | 18 A |
| DC Output +12V (#1) | 18 A | 38 A | 38 A |
| DC Output +12V (#2) | 18 A | n/a | n/a |
| DC Output +12V (#3) | 18 A | n/a | n/a |
| DC Output +12V (#4) | 18 A | n/a | n/a |
| DC Output -12V | 0.3 A | 0.5 A | 0.5 A |
| DC Power +12V Combined | 456 W | 456 W | 456 W |
| PFC | active | active | active |
| Specified Hold-Up Time | 19 ms | > 17 ms | 16 ms |
| MTBF | 300 000 hours | > 100 000 hours | 50 000 hours |
| Cooling Specifications | |||
| Main Fan | 135 mm | N/A | N/A |
| Main Fan Speed | up to 1200 RPM | N/A | N/A |
| Secondary Fan | N/A | N/A | N/A |
| Secondary Fan Speed | N/A | N/A | N/A |
| Connectors | |||
| 20+4 pin Motherboard | 1x (55 cm) | 1x (60 cm) | 1x (55 cm) |
| CPU | 1x (55 cm) | 1x (65 cm) | 1x 55 cm) |
| PCI Express 6-pin/6+2-pin (Graphics) | 0/2x (55 cm) | 0/2 (60 cm) | 1/1x (55-70 cm) |
| Molex 4-pin (Peripherals) | 4x (85–100 cm) | 5x (45-75 cm) | 6x (50–80 cm) |
| SATA Power | 8x (55–100 cm) | 5x (45-75 cm) | 6x (50–80 cm) |
| 4-pin Floppy | 1x (115 cm) | 2x (90 cm) | 2x (95 cm) |
| Product Specifics | |||
| Accessories | Screws, Velcro Strips, Cables Ties | Screws, Velcro Strips, Cables Ties | Screws, Velcro Strips, Cables Ties |
| Cable Management | Yes | Yes, Fully Modular | No |


























