If you want a computer to truly be silent, you need to use passive cooling components. Whereas passive cooling components are more frequently available in the graphics card and CPU sector, they are something of a niche market when it comes to power supplies. This is not really a surprise though, given that purely passive units are considerably more expensive than those with fans, and they generally provide relatively poorer performance as well.
Our test compares the Zen 400 from Fortron (FSP) with a power output of 400 watts, and the Nightjar 450 from Silverstone which provides a maximum of 450 watts. Both models can be purchased for less than $200.

In order to ensure proper comparison of the units—and in anticipation of future testing with other units having different power output levels—we tested the efficiency at 100%, 50% and 20% load. In the future, we will also be testing the efficiency at an output of 250 watts, as well as an extremely low output of just 35 watts. The latter is of particular importance for low power systems, to ensure that users are able to find the right kind of power supply for these as well.
The Zen 400 from Fortron, with its output of 400 watts, stands out immediately thanks to its blue color. Compared to its 300 watt predecessor, the first thing you notice is a large aluminum cooling element on the underside of the unit, which is reflected in its considerably higher weight.
There is a single 6-pin connection for graphics cards. The ATX connection corresponds to the ATX12V 2.2 standard; it has 24 pins and can be split to accommodate older motherboards.
The unit’s connections are no longer up-to-date. It only has four SATA connections, yet these are becoming more and more important. Oddly, there are still six of the 4-pin Molex connections used by older drives. There are also two floppy connections on the power supply, though these can be used for fan controllers. The +12V CPU connection is only available as 4-pin version, which can lead to problems with some boards that require an 8-pin connection.
The length of the connection cables also leaves a lot to be desired: only 16” (40 cm) to the ATX connection. This may be too short for larger cases, and as a result, it may not be possible to route the cables as neatly as one would like.
On the rear of the power supply you’ll find the IEC socket and a blue illuminated main switch. The latter is of particular importance, as a user operating a passive power supply cannot hear whether or not it is switched on. There are no other indicators showing the operational status of the unit.
The power supply is a full range unit that can be operated on a voltage ranging between 110 V and 240 V. There is no need to manually switch between the voltage ranges.
The output of the power supply is 400 watts, and 560 watt peaks are possible for short periods of time. The combined performance of the 3.3 V and 5 V rails is a maximum of 130 watts.
During use, the power supply makes its presence known by a high-pitched, high-frequency noise that occurs most often when under heavy use. Up to a load of approximately 250 watts this noise can hardly be heard, but the higher the load gets, the louder the noise. This is a very annoying noise that detracts from the "silent PC" concept.
With no additional ventilation, constant operation under full load at 400 watts is not possible. The power supply switches itself off due to overheating after approximately two hours. A level of 300 watts, however, can be maintained permanently. A minimal movement of air in the computer case—such as a slowly rotating 120 mm fan—enables the device to be operated permanently at high load.
The test with the D201GLY2 board from Intel was not a problem—this kind of mini ITX board often causes problems with power supplies.
The output voltages ranged within the permitted values for the entire duration of the test period. In particular, the important 3.3 V, 5 V and 12 V voltage rails only deviated by a few millivolts from the nominal values. Only under full load were there slightly increased breaks in voltages, which were again well within the specification.
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.22 V | 3.14 V to 3.47 V |
| 5 V | 4.96 V | 4.75 V to 5.25 V |
| 12 V | 11.88 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 11.82 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 4.87 V | 4.75 V to 5.25 V |
| -12 V | -12.51 V | -10.80 V to -13.20 V |
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.28 V | 3.14 V to 3.47 V |
| 5 V | 5.01 V | 4.75 V to 5.25 V |
| 12 V | 11.95 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 11.93 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 4.90 V | 4.75 V to 5.25 V |
| -12 V | -11.80 V | -10.80 V to -13.20 V |
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.31 V | 3.14 V to 3.47 V |
| 5 V | 5.05 V | 4.75 V to 5.25 V |
| 12 V | 11.99 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 11.98 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 4.92 V | 4.75 V to 5.25 V |
| -12 V | -11.41 V | -10.80 V to -13.20 V |
Efficiency plays an ever-increasingly important role in modern computers. Particularly with HTPCs designed to run constantly in living rooms, the high level of efficiency of the power supply ensures significantly lower electricity costs at the end of the year.
Overall, the Fortron power supply performed well. In the three load stages of the specification, the unit was constantly at over 84%. The best performance was obtained at below half load, where the efficiency increased to over 88%.
In our fictional system with a 250 watt load, the efficiency remained at a very good 87.7%, but in our low power system it only managed 76.3%.
In standby mode, with no load at all, the power supply only used 440 mW. With a standby load of just 2.5 W (500 mA at 5 V standby voltage) the Fortron converter drew 3.77 W from the socket, which is an efficiency of 65.5%.
The Zen 400 (PPA4000300) from Fortron (FSP) is available for a price of around $150.
The Nightjar 450 from Silverstone, which is also listed in shops under the name ST45NF, has a maximum nominal performance rating of 450 watts (a higher peak load is not specified by the manufacturer). The basic construction of the power supply, with a large aluminum cooling element, corresponds to that of the Fortron unit.
When it comes to connections, Silverstone has invested in the future somewhat. As a result, there are six SATA connections on the unit, along with six 4-pin Molex connections. The white-grey color combination reminds you of days gone by, but when hunting around in a tower for the right connections, you realize that the different SATA connection colors are practical.
The CPU connection is split, and can thus be used to suit both four- and eight-pin requirements. Silverstone has also employed this method for the PCIe connections: two six-pin connections are available, one of which can be extended to an eight-pin connection for modern graphics cards. The ATX connection is split in this way, and offers options with both 24-pin and 20-pin connections.
Silverstone has also not scrimped on the cable lengths; the ATX connection has a cable over 21” (55 cm) in length.
On the rear of the power supply there is an IEC socket and an non-illuminated main switch, as well as two LEDs that indicate the operational status of the power supply.
Whereas the top LED shows the temperatures—at over 55°C the usually green LED switches to yellow—the lower LED tells you whether the unit is in standby (orange), switched on (green) or cannot be switched on due to a fault (red). The latter occurs, for example, when the power supply has overheated and deactivated itself.
Unlike the Fortron Zen, the Silverstone unit is silent—even under the highest load—and does not make any whirring noises.
If the unit is placed under a load of 450 watts without ventilation, it switches itself off automatically after about two hours due to overheating, but at an output of 330 watts, we were able to operate it constantly. As with the Fortron unit, a very low flow of air is sufficient to enable constant operation even under a full load of 450 watts.
The Silverstone Nightjar was also able to operate our D201GLY2 board from Intel with no trouble at all.
The Silverstone Nightjar makes no mistakes when it comes to voltages either. All values were always within the permitted ranges set out by the ATX12V specification.
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.15 V | 3.14 V to 3.47 V |
| 5 V | 4.91 V | 4.75 V to 5.25 V |
| 12 V | 11.99 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 11.94 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 4.95 V | 4.75 V to 5.25 V |
| -12 V | -12.27 V | -10.80 V to -13.20 V |
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.23 V | 3.14 V to 3.47 V |
| 5 V | 4.98 V | 4.75 V to 5.25 V |
| 12 V | 12.09 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 12.07 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 5.00 V | 4.75 V to 5.25 V |
| -12 V | -11.70 V | -10.80 V to -13.20 V |
| Nominal Value | Measurement | Permitted Deviation |
|---|---|---|
| 3.3 V | 3.28 V | 3.14 V to 3.47 V |
| 5 V | 5.02 V | 4.75 V to 5.25 V |
| 12 V | 12.15 V | 11.40 V to 12.60 V |
| 12 V (CPU) | 12.14 V | 11.40 V to 12.60 V |
| 5 V (Standby) | 5.03 V | 4.75 V to 5.25 V |
| -12 V | -11.56 V | -10.80 V to -13.20 V |
Under full load, the efficiency of 87.3% is the same as the Fortron unit, while at medium and lower loads, it is a mere 1% worse than its competitor.
The direct comparison using our fictional 250 watt system showed marginal differences, with the 87% output of the Silverstone Nightjar is again on a par. The biggest differences could be seen with our low power system. Here, the Silverstone converter performed at 71.5%, almost 5% below the Zen 400 unit.
Even in standby mode, the Silverstone unit couldn’t do any better. Without load, the power supply uses 2.57 watts, probably due to the LEDs and their controller. Even with load on the standby cable, the result is pretty unimpressive. The power supply draws almost 6 watts of power in order to make 2.5 watts of output available. The result is a marginal efficiency of 42.7%.
The Silverstone power supply is a fair bit more expensive, priced online around $200.






Our results favor Silverstone’s Nightjar. At medium and high outputs, the efficiency is very high, and the unit cannot be heard even under full load. Also advantageous are connection cables at sensible lengths, which also enable use in larger cases, and flexible connection options with the separable 8-pin connections for CPU and graphics card.

The less expensive power supply from Fortron only gains points for operation with low power systems, which work with outputs in the 50 watt to 150 watt range—at higher output ranges the power supply starts to emit a bothersome high-pitched noise. On the other hand, the constantly high efficiency and low standby power consumption are notable.

