Test Setup

All measurements were performed using ten electronic loads (seven Array 3711A [300 W each] and three Array 3710A [150 W each]), which are able to deliver over 2500 W of load and are controlled by a custom-made software. We also used a Picoscope 3424 oscilloscope, a CHY 502 thermometer, a Fluke 175 multimeter, and an Instek GPM-8212 power meter. Furthermore, in our setup, we included a wooden box, which, along with a heating element, was used as a hot box. Finally, we had at our disposal four more oscilloscopes (Rigol 1052E and VS5042, Stingray DS1M12, and a second Picoscope 3424) and a CEM DT-8852 sound level meter. In this article, you will find more details about our equipment and the review methodology we follow. Finally, if the manufacturer states that the maximum operating temperature of the test unit is only 40°C, then we try to stay near this temperature; otherwise, we crank up the heat inside the hotbox up to 45-50°C.

Voltage Regulation Charts

The following charts show the voltage values of the main rails, recorded over a range from 60W to the maximum specified load, and the deviation (in percent) for the same load range.

5VSB Regulation Chart

The following chart shows how the 5VSB rail deals with the load we throw at it.

Efficiency Chart

In this chart, you will find the efficiency of the Fortress 550W at low loads and at loads equal to 20-100% of the PSU's maximum rated load.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the Fortress 550W. The applied load was equal to (approximately) 20%, 40%, 50%, 60%, 80%, and 100% of the maximum load that the PSU can handle. In addition, we conducted two more tests. In the first test, we stressed the two minor rails (5V and 3.3V) with a high load, while the load at +12V was only 2A, and, in the second test, we dialed the maximum load that the +12V rail could handle, while the load on the minor rails was minimal.


The PSU features a very cool operation and we had to leave the heat elements of the hot box constantly on in order to raise the ambient temperature close to 50°C. Also, even at the worst case, the output noise of the unit's fan was very low, almost inaudible. This was also verified by the small difference between the input and output temperature on the corresponding column of the table above. Since the fan's RPMs remained low, the delta at all cases was small.
Regarding performance, you can see that efficiency was very high throughout all load ranges and peaked at an impressive 93% reading with 40% load. On top of that, voltage regulation was tight overall, especially at +12V, proving that ATNG delivered an amazing platform to Rosewill. This PSU is a solid performer, and if it manages to keep clean outputs (low ripple), it will surely pose a threat to the competition.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the Fortress 550W at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dialed were 40, 60, 80, and 100W (for PSUs with over 500W of capacity). This is important for settings where the PC is in idle mode with power saving turned on.


So far, among the numerous PSUs we have tested, only the Super Flower Golden King 500W and the Kingwin Absolute Platinum 550W, two PSUs based on exactly the same platform, managed to register a higher efficiency than the Fortress 550W at such low loads. Even with just 40W, efficiency is over 80% and with a 100W load it reaches 89%. This is simply amazing!

5VSB Efficiency

The ATX spec states that the 5VSB standby supply's efficiency should be as high as possible and recommends 50% or higher efficiency with 100mA of load, 60% or higher with 250mA of load, and 70% or higher with 1A or more of load.
We will take four measurements: three at 100, 250, and 1000 mA, and one with the full load that the 5VSB rail can handle.


The efficiency of 5VSB is good overall, although not among the highest we have seen so far. Nevertheless, it is highly satisfactory.

Power Consumption in Idle and Standby Mode

In the table below, you will find the power consumption and the voltage values of all rails (except -12V) when the PSU is in idle mode (powered on but without any load on its rails) and the power consumption when the PSU is in standby mode (without any load at 5VSB).


Vampire power is low and the unit easily meets the ErP Lot 6 2010 and the future 2013 requirements. This is something nice for your pocket and for the environment since only a very small amount of energy goes wasted.