Gigabyte UD850GM Power Supply Review

The Gigabyte UD850GM survived all of our tough tests.

Gigabyte UD850GM
(Image: © Tom's Hardware)

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Primary Rails And 5VSB Load Regulation

The following charts show the main rails' voltage values recorded between a range of 40W up to the PSU's maximum specified load, along with the deviation (in percent). Tight regulation is an important consideration every time we review a power supply because it facilitates constant voltage levels despite varying loads. Tight load regulation also, among other factors, improves the system's stability, especially under overclocked conditions. It also applies less stress to the DC-DC converters that many system components utilize.

Load regulation is tight at 12V, but loose on the minor rails. 

Hold-Up Time

Put simply; hold-up time is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption.

The hold-up time is longer than 17ms, and the power ok signal is accurate and longer than 16ms. 

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. A large enough inrush current can cause circuit breakers and fuses to trip. It can 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.

Inrush current is at normal levels with 115V but rather high with 230V. 

Leakage Current

In layman's terms, leakage current is the unwanted energy transfer from one circuit to another. In power supplies, it is the current flowing from the primary side to the ground or the chassis, which in the majority of cases is connected to the ground. We use a GW Instek GPT-9904 electrical safety tester instrument to measure leakage current.

The leakage current test is conducted at 110% of the DUT's rated voltage input (so for a 230-240V device, we should conduct the test with 253-264V input). The maximum acceptable limit of a leakage current is 3.5 mA and it is defined by the IEC-60950-1 regulation, ensuring that the current is low and will not harm any person coming in contact with the power supply's chassis.

Gigabyte UD850GM

(Image credit: Tom's Hardware)

Leakage current is low. 

10-110% Load Tests

These tests reveal the PSU's load regulation and efficiency levels under high ambient temperatures. They also show how the fan speed profile behaves under increased operating temperatures.

Swipe to scroll horizontally
Test12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])Temps (In/Out)PF/AC Volts
10%5.230A1.961A1.947A0.999A84.99886.584%0<6.044.67°C0.947
12.121V5.099V3.39V5.007V98.16540.23°C115.11V
20%11.474A2.947A2.928A1.201A169.94189.903%0<6.045.26°C0.966
12.117V5.09V3.381V4.996V189.02240.45°C115.1V
30%18.079A3.445A3.422A1.404A254.9590.774%97928.341.49°C0.977
12.108V5.081V3.375V4.986V280.87746.85°C115.07V
40%24.700A3.944A3.92A1.608A340.03791.254%98128.341.68°C0.98
12.098V5.071V3.368V4.976V372.62747.58°C115.05V
50%30.974A4.939A4.912A1.813A424.99191.049%98328.441.86°C0.984
12.090V5.062V3.359V4.965V466.77148.37°C115.02V
60%37.232A5.938A5.91A2A509.44690.673%98728.642.2°C0.986
12.079V5.053V3.351V4.954V561.84649.29°C115.01V
70%43.571A6.942A6.912A2.226A594.90290.115%110631.743.76°C0.987
12.067V5.043V3.342V4.942V660.16651.31°C114.98V
80%49.910A7.949A7.919A2.332A679.74889.311%176642.143.86°C0.988
12.059V5.034V3.334V4.932V761.09852.02°C114.96V
90%56.660A8.462A8.418A2.438A765.18188.56%208745.944.52°C0.989
12.049V5.024V3.326V4.924V864.02153.65°C114.93V
100%63.175A8.974A8.957A3.062A849.95987.614%212146.245.22°C0.991
12.034V5.015V3.316V4.9V970.11555.22°C114.91V
110%69.561A9.992A10.072A3.067A934.58286.75%211946.246.9°C0.992
12.023V5.004V3.306V4.892V1077.34257.77°C114.88V
CL10.116A12.402A12.378A0A106.30683.852%0<6.048.23°C0.954
12.121V5.096V3.369V5.011V126.7841.7°C115.12V
CL20.115A19.646A0A0A101.39882.183%0<6.050.52°C0.953
12.127V5.09V3.367V5.022V123.38142.55°C115.12V
CL30.115A0A19.579A0A67.39377.569%0<6.052.217°C0.938
12.121V5.072V3.371V5.007V86.88943.06°C115.13V
CL470.588A0A0A0.001A849.68988.373%211246.144.18°C0.991
12.037V5.009V3.326V4.979V961.48254.21°C114.91V

The PSU doesn't have a problem with high loads and challenging conditions. We pushed it hard, and it didn't budge, so the reliability problems of the past appear to be resolved.

20-80W Load Tests

In the following tests, we measure the PSU's efficiency at loads significantly lower than 10% of its maximum capacity (the lowest load the 80 PLUS standard measures). This is important for representing when a PC is idle with power-saving features turned on.

Swipe to scroll horizontally
Test12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])Temps (In/Out)PF/AC Volts
20W1.226A0.49A0.486A0.199A19.99770.236%0<6.040.23°C0.867
12.117V5.099V3.396V5.03V28.47237.14°C115.13V
40W2.700A0.687A0.681A0.298A39.99679.921%0<6.040.82°C0.908
12.106V5.097V3.394V5.027V50.0537.48°C115.12V
60W4.172A0.883A0.875A0.398A59.99584.027%0<6.042.65°C0.932
12.112V5.095V3.393V5.023V71.40138.91°C115.12V
80W5.638A1.079A1.07A0.498A79.94487.157%0<6.043.01°C0.943
12.117V5.096V3.392V5.019V91.72438.94°C115.12V

The cooling fan doesn't spin at light loads. 

2% or 10W Load Test

The ATX spec requires 60% and higher efficiency with 115V input. The applied load is only 10W for PSUs with 500W and lower capacities, while for more robust units, we dial 2% of their max-rated capacity.

Swipe to scroll horizontally
12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])Temps (In/Out)PF/AC Volts
1.240A0.222A0.222A0.053A17.16867.767%0<6.030.36°C0.854
12.108V5.097V3.397V5.034V25.33228.1°C115.15V

Efficiency with 2% load is over 60%, meeting the newest ATX spec's requirements. 

Efficiency & Power Factor

Next, we plotted a chart showing the PSU's efficiency at low loads and loads from 10 to 110% of its maximum rated capacity. The higher a PSU's efficiency, the less energy goes wasted, leading to a reduced carbon footprint and lower electricity bills. The same goes for Power Factor.

The platform is highly efficient with normal loads, but there is room for improvement in lower modes. 

5VSB Efficiency

Swipe to scroll horizontally
Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts
10.1A0.504W74.624%0.092
5.035V0.675W115.15V
20.25A1.258W78.625%0.195
5.033V1.6W115.14V
30.55A2.765W80.038%0.317
5.027V3.455W115.14V
41A5.019W80.502%0.4
5.017V6.235W115.14V
51.5A7.513W80.673%0.436
5.007V9.313W115.14V
63A14.93W78.897%0.484
4.976V18.923W115.13V

The 5VSB rail is highly efficient. 

Power Consumption In Idle And Standby

Swipe to scroll horizontally
Mode12V5V3.3V5VSBWattsPF/AC Volts
Idle12.104V5.099V3.4V5.037V8.2390.653
115.15V
Standby0.0320.008
115.15V

Vampire power is high with 230V input. It should be lower than 0.1W. 

Fan RPM, Delta Temperature, And Output Noise

All results were obtained between an ambient temperature of 37 to 47 degrees Celsius (98.6 to 116.6 degrees Fahrenheit).

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

The fan speed profile is aggressive at high temperatures. However, given the unknown caps on the secondary side, we wouldn't suggest a relaxed speed profile. 

The following results were obtained at 30 to 32 degrees Celsius (86 to 89.6 degrees Fahrenheit) ambient temperature.       

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

The passive mode doesn't last long at average operating temperatures, close to 30 degrees Celsius. It has been in the 25-30 dBA range for quite a long and exceeds 40 dBA with over 700W loads. 

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Aris Mpitziopoulos
Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.