Fortron-Source Zen fanless 300W ATX12V power supply

Viewing page 4 of 5 pages. Previous 1 2 3 4 5 Next


For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

In the test rig, the ambient temperature of the PSU varies proportionately with its output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a precise high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various standard loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches >40°C at full power. This is impossible to achieve with an open test bench setup.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise results obtained here still cannot be considered absolute. There are far too many variables in PCs and far too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you've never met. You'll probably get a reasonable overall representation of that person, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: While our testing loads the PSU to full output (even >600W!) in order to verify the manufacturer's claims, real desktop PCs simply do not require anywhere near this level of power. The most pertinent range of DC output power is between about 65W and 250W, because it is the power range where most systems will be working most of the time. To illustrate this point, we recently conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most powerful P4-3.2 Gaming rig drew ~180W DC from the power supply under full load ? well within the capabilities of any modern power supply. Please follow the link provided above to see the details. It is true that very elaborate systems with SLI could draw as much as another 150W, but the total still remains well under 400W in extrapolations of our real world measurements.


It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

  • Intake temperature (determined by ambient temperature and power output level)
  • Efficiency of the PSU (how much heat it generates while producing the required output)
  • The effectiveness of the PSU's cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only number that is comparable between different reviews, as it is unaffected by the ambient temperature.

Because the side of the Zen is open, the top and the side of the test rig was covered up with cardboard to simulate the walls of an actual case. This ensured that only the rear vent is exposed to the external air, as it would be in a real system.

Ambient conditions during testing were 25°C and 20 dBA, with input of 120 VAC / 60 Hz measured at the AC outlet. It was a couple of degrees warmer than usual in the lab, and the Intake Temp readings in the measured data table below reflects this.

DC Output (W)
AC Input (W)
Intake Temp (°C)
PSU Exhaust (°C)
Temperature Rise (°C)
Power Factor
NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.


1. VOLTAGE REGULATION was excellent, within ¬Ī1% on the +12V and +5V lines in any combination of loads. The +3.3V line strayed by a maximum of 2%. This is very impressive performance.

  • +12V: 11.89 to 12.04
  • +5V: 4.96 to 5.00
  • +3.3V: 3.35 to 3.38

The AC power draw also remained very stable. The AC power draw for most power supplies begins to fluctuate as it approaches full load, often by as much as 10~20W. The Zen, on the other hand, drew exactly 342W at full load ? no more, no less. The stability of both the AC power draw and the output voltage regulation inspires our confidence in the quality of the design.

2. EFFICIENCY was excellent, although we did not quite reach see the claimed 89%. It is likely that this efficiency could be reached if a 240VAC input voltage was used. Most impressive is the efficiency at low output: This is the first power supply we have tested that measured 80% efficient at the low 65W load. As the load increases, efficiency also goes up. Peak efficiency was achieved at 300W output.

This performance is on par with the best we have measured: The Antec Phantom 500. Although the Phantom is slightly more efficient under higher loads, the Zen is more efficient below 150W ? the range in which it is most likely to be used. These differences are minor, however, and are always within a percentage point or two. The differences may lie within the resolution capability of our test setup.

3. POWER FACTOR was lower than we usually expect of active power factor correction, although still very good compared to passive or no PFC. Once the total load rose to 150W and above, power factor quickly approached the ideal value of 1.0.


The Zen is fanless, so the noise generated by the power supply was minimal. No electrical noise was noticed during the course of the testing, which cannot be said of some of the other fanless models on the market. There was no hum, buzz or squeal that could be heard from any distance. A trace amount of something was barely audible to Mike when he pressed his ear right up against the cover. For all practical purposes, the Zen is silent.


The temperature rise within the power supply was in line with the other fanless power supplies we've tested. Although a 20°C rise at 300W output is hardly stellar thermal performance for a fanned power supply, it's fairly typical for a fanless model. Warm air could be felt coming out of the rear vent throughout testing, which shows that there was airflow through the power supply even though it has no active source of airflow. We can attribute most of this airflow to the internal airflow within our test rig. The overall stability of the power supply gave us no reason to think that its internal cooling was inadequate.

Previous 1 2 3 4 5 Next

Power - Article Index
Help support this site, buy from one of our affiliate retailers!