Test Setup

All measurements are performed using two Chroma 6314A mainframes equipped with the following electronic loads: six 63123A [350 W each], one 63102A [100 W x2], and one 63101A [200 W]. The aforementioned equipment is able to deliver 2500 W of load, and all loads are controlled by a custom-made software. The AC source is a Chroma 6530 capable of delivering up to 3 kW of power. We also use a Keysight DSOX3024A oscilloscope, a Rigol DS2072A oscilloscope kindly sponsored by Batronix, a Picoscope 3424 oscilloscope, a Picotech TC-08 thermocouple data logger, two Fluke multimeters (models 289 and 175), a Keithley 2015 THD 6.5 digit bench DMM, and a lab grade N4L PPA1530 3-phase power analyzer along with a Yokogawa WT210 power meter. We also include a wooden box, which, along with some heating elements, is used as a hot box. Finally, we have at our disposal three more oscilloscopes (Rigol VS5042, Stingray DS1M12, and a second Picoscope 3424), and a Class 1 Bruel & Kjaer 2250-L G4 Sound Analyzer equipped with a Type 4955a microphone that features a 6.5-110 dBA-weighted dynamic range on paper (it can actually go even lower, at 5 dB[A]). You will find more details about our equipment and the review methodology we follow in this article. We also conduct all of our tests at 40–45 °C ambient to simulate the environment seen inside a typical system more accurately, with 40–45 °C being derived from a standard ambient assumption of 23 °C and 17–22 °C being added for the typical temperature rise within a system.

To control the Chroma 6530 source, we use a GPIB-USB controller, which avoids its extra picky Serial port. This controller was kindly provided by Prologix.



To protect our very expensive Chroma AC source, we use an FSP Champ online UPS with a capacity of 3000VA/2700W.

Primary Rails Load Regulation

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

5VSB Regulation

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

Hold-up Time

Hold-up time is a very important PSU characteristic and represents the amount of time, usually measured in milliseconds, a PSU can maintain output regulations as defined by the ATX specification without input power. In other words, it is the amount of time the system can continue to run without shutting down or rebooting during a power interruption. The ATX spec sets the minimum hold-up time to 17 ms with the maximum continuous output load.

According to the ATX spec, the PWR_OK is a "power good" signal. This signal should be asserted as high, at 5 V, by the power supply to indicate that the +12 V, 5 V, and 3.3 V outputs are within the regulation thresholds and that sufficient mains energy is stored by the APFC converter to guarantee continuous power operation within specification for at least 17 ms. Conversely, PWR_OK should be de-asserted to a low state, 0 V, when any of the +12 V, 5 V, or 3.3 V output voltages falls below the under-voltage threshold, or when mains power has been removed for a sufficiently long time such that the power supply's operation cannot be guaranteed. The AC loss to PWR_OK minimum hold-up time is set at 16 ms, which is less than the hold-up time described in the paragraph above because the ATX spec sets a PWR_OK inactive to DC loss delay which should be more than 1 ms. This means that the AC loss to PWR_OK hold-up time should be lower than the overall hold-up time of the PSU, and this ensures that the power supply will not send a power good signal while any of the +12 V, 5 V and 3.3 V rails are out of spec.

In the following screenshots, the blue line is the mains signal, the green line is the "Power Good" signal, and the yellow line represents the +12V rail.







Hold-up time is long, and the power-ok signal is accurate. We also had a second MX650 sample which registered a notably lower hold-up time even though it uses the same parts. We can't explain why the first sample has a hold-up time of 24.5 ms, while the second only has a hold-up time of 18.4 ms, especially since this is a 6.1 ms difference! The bulk cap in the second sample was most likely not in its best shape.

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input current drawn by an electrical device when it is first turned on. Because of the charging current of the APFC capacitor(s), PSUs produce a lot of inrush-current right as they are turned on. A lot of inrush current can cause the tripping of circuit breakers and fuses and may also damage switches, relays, and bridge rectifiers; as a result, the lower the inrush current of a PSU right as it is turned on, the better.


The inrush current is at normal levels.

Load Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the MX650's efficiency. The applied load was equal to (approximately) 10%-110% of the maximum load the PSU can handle, in 10% steps.

We conducted two additional tests. In the first test, we stressed the two minor rails (5 V and 3.3 V) with a high load while the load at +12V was only 0.10 A. This test reveals whether the PSU is compatible with Intel's C6 and C7 sleep states or not. In the second test, we dialed the maximum load the +12V rail can handle while the load on the minor rails is minimal.


Load regulation, while tight on the +12V, 5V and 3.3V rails, is still no match for the Seasonic Prime Fanless, which uses a superior platform. Efficiency levels are high, however, and we didn't notice a notable drop with the 100% and 110% loads, as is usually the case with most PSUs. Finally, the PSU handled the increased operating temperatures easily, which shows that it can handle tough situations without breaking a sweat.