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Zalman ZM750-EBT PSU Review

Zalman's new EBT line consists of four PSUs ranging from 650W to 1kW capacity. Today, we're testing the ZM750-EBT, which, thanks to a low price, achieves a good value score. But how does it fare in terms of absolute performance?

Load Regulation, Hold-Up Time And Inrush Current

To learn more about our PSU tests and methodology, please check out How We Test Power Supply Units. 

Primary Rails And 5VSB Load Regulation

Load Regulation testing is detailed here.

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Hold-Up Time

Our hold-up time tests are described in detail here.

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Not only are we measuring the PWR_OK signal (AC loss to PWR_OK hold-up time), but we're also checking when the +12V rail drops below its limit when AC voltage is removed from the PSU.

Our oscilloscope measured only 9.2ms, while the ATX spec requires at least 17ms. In other words, Zalman's PSU fails big time in this test. Meanwhile, the AC loss to PWR_OK hold-up time was extra long, exceeding 27ms. Sirfa uses a nasty trick here, and in the following paragraph, we'll try to explain what it did plainly.

Normally, the PWR_OK signal has to drop to zero volts before any of the rails fall below the corresponding ATX limit. In this case, the PWR_OK signal is kept active for a much longer period. This means that very low DC outputs feed your precious hardware, since the motherboard sees the PSU as active through the PWR_OK signal. In some cases, this can cause damage. Instead of dropping to zero volts while the +12V rail was higher than 11.4V, the ZM750-EBT's PWR_OK dropped while the 12V rail was at just 10.24V!

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The time difference between the moment when PWR_OK drops to zero and the +12V rail goes out of spec is very large at 15ms. Normally, the PWR_OK signal should drop before the +12V rail goes out of limits, not after.

Inrush Current

For details on our inrush current testing, please click here.

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The inrush current is very high with both 230V and 115V input.

Load Regulation And Efficiency Measurements

The first set of tests reveals the stability of the voltage rails and the PSU's efficiency. The applied load equals (approximately) 10 to 110 percent of the maximum load the supply can handle, in increments of 10 percentage points.

We conducted two additional tests. During the first, we stressed the two minor rails (5V and 3.3V) with a high load, while the load at +12V was only 0.10A. This test reveals whether a PSU is Haswell-ready or not. In the second test, we determined the maximum load the +12V rail could handle with minimal load on the minor rails. 

Test12V5V3.3V5VSBDC/AC (W)EfficiencyFanSpeed (RPM)FanNoise (dB[A])Temps In/Out (°C)PF/AC Volts

Load regulation on the +12V and 5VSB rails is satisfactory for a PSU with this price tag. At 5V it's decent, and 3.3V is on the loose side, exceeding 3% deviation.

As far as efficiency goes, the ZM750-EBT clears our 20 percent test by registering over 87% efficiency. However, it fails to do so in the 50 percent and full load tests. Of course, we run our benchmarks at much higher ambient temperatures than the 80 Plus organization and, in general, those conditions seriously affect efficiency. Still, we've seen other Gold-rated units register much higher efficiency in the same metrics.

Finally, output noise is very high since Sirfa uses an aggressive fan profile. If you dislike fan noise and plan to push your machine hard, this power supply probably won't work for you.