Test Setup

All measurements are performed utilizing ten electronic loads (seven Array 3711A, 300W each, and three Array 3710A, 150W each), which are able to deliver over 2500W of load and are controlled by a custom made software. We also use a Picoscope 3424 oscilloscope, a CHY 502 thermometer, a Fluke 175 multimeter and an Instek GPM-8212 power meter. Furthermore, in our setup we have included a wooden box, which along with a heating element is used as a Hot Box. Finally, we have 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 CAPSTONE-750-M at low loads and at loads equal to 20-100% of PSU’s maximum rated load.

Voltage Regulation and Efficiency Measurements

The first set of tests reveals the stability of voltage rails and the efficiency of CAPSTONE-750-M. The applied load equals to (approximately) 20%, 40%, 50%, 60%, 80% and 100%, of the maximum load that the PSU can handle. In addition, we conduct two more tests. In the first we stress the two minor rails (5V & 3.3V) with a high load, while the load at +12V is only 2A and in the second test we dial the maximum load that +12V can handle while load at minor rails is minimal.

During the full load test we got over-excited and let the ambient inside the hotbox hit 52.5°C! This is a really high temperature at which most units would shut down or even blow up, but the Capstone PSU kept on working normally, delivering full load! This is something we don't see every day and proves that this PSU will tolerate heavy abuse without complaining. Efficiency even at such high operating temperatures is very high and more than worthy of the 80 Plus Gold levels.
Regarding voltage regulation, at +12V it's within 2% range, at 5V it's a little above 3%, at 3.3V it's on the loose side registering a well over 4% deviation while the 5VSB rail registered one of the best voltage regulations we have seen up to date. Finally throughout all tests the unit's fan was operating fairly quietly, meaning that during testing we had to go really close to the hot box to hear it operating while from about one meter distance it was barely audible. Taking into account that it was working at full speed most of the time, due to the high ambient temperatures, at normal conditions it will pass unnoticeable.

Efficiency at Low Loads

In the next tests, we measure the efficiency of CAPSTONE-750-M at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dial are 40, 60, 80 and 100W (for PSUs with over 500W capacity). This is important for scenarios in which a typical office PC is in idle with power saving turned on.

At low loads the unit registered excellent efficiency readings, since in three out of the four tests we conducted it easily passed the 80% mark. With the new energy saving techniques that significant drop energy consumption at low system utilization, efficiency at such low loads surely comes in handy and saves you from unnecessary energy waste.

5VSB Efficiency

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

At 5VSB efficiency is close to the corresponding levels that the ATX spec sets, so there is pretty much nothing noteworthy to comment here. Except of course the good voltage regulation that this rail registered.

Power Consumption in Idle & Standby

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 (On but without any load at its rails) and the power consumption when the PSU is in standby (without any load at 5VSB).

Phantom power is kept low, below 0.5W so this unit meets the stricter, future, ErP Lot 6 2013 directive. The use of efficient standby PWM controllers greatly reduces energy consumption at standby and it is truly impressive that such low cost ICs manage to achieve so much in terms of energy savings.