Efficiency

Using the efficiency results from the previous page, we plotted a chart showing efficiency of the CMX850 at low loads and at loads equal to 20%-110% of the PSU's maximum-rated load.



The CMX850 easily meets the competition in efficiency, and it even managed to outperform a worthy opponent, the Antec HCG-850M.

Efficiency at Low Loads

The next tests measure the efficiency of the CMX850 at loads much lower than 20% of its maximum-rated load (the lowest load the 80 Plus Standard measures). The loads we dialed were 40 W, 60 W, 80 W, and 100 W (for PSUs with over 500 W of capacity). This is important for settings where the PC is in idle mode with Power Saving turned on.

At low loads, efficiency is pretty good considering this is a Bronze unit with a relatively high capacity—stronger Bronze units normally perform worse in these tests. Here we should stress that most systems spend significant amounts of time at low utilization or idle state efficiency, making this load range quite important, so don't take the results here lightly by only paying attention to normal load tests instead.

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 100 mA of load, 60% or higher with 250 mA of load, and 70% or higher with 1 A or more of load.

We will take four measurements: one at 100, 250, and 1000 mA each, and one with the full load the 5VSB rail can handle.

The 5VSB rail registered average efficiency readings which, however, meet ATX requirements. We didn't expect more, though having the last two readings edge closer to 80% mark would be nice.

Power Consumption in Idle & Standby

The table below will give you the power consumption and 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 on 5VSB).

Phantom power was low and easily met the requirements of the ErP Lot 6 2013 directive.

Fan RPM, Delta Temperature & Output Noise

The following charts illustrate the cooling fan's speed (RPMs) and the delta difference between input and output temperature. These results were obtained at 39°C-46°C ambient.



A chart that shows the cooling fan's speed (RPMs) and the output noise follows. We measure the fan's noise from 1 meter away, inside a small custom-made anechoic chamber whose internals are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). The background noise inside the anechoic chamber was below 30 dBA during testing, and the results were obtained with the PSU operating at 39°C-46°C ambient.



The following graph illustrates the fan's output noise throughout the entire operating range of the PSU. The same conditions of the above graph apply to our measurements, but the ambient in this case was between 28°C and 30°C.



The PSU was quite noisy at even below 30°C while in operation, so it won't be a suitable candidate for a system equipped with silent components.