What is the problem with cheap Chinese PSU’s? Well two reasons and they being :

1) Does no comply with any safety requirements

2) Will fail to meet any EMC requirements

Lets have a look at the first point, safety. There are two PSU’s below, one the cheap Chinese and the other a quality one.

There are other markings on the approved PSU such as UL and CE, just noticed the non approved PSU does not have a CE mark.

So that cover the safety side of this… Now EMC.

Conducted Emissions was performed using both PSU’s. The power supplies were powering an EUT for the duration of the tests. The test specification used was BS EN55032:2015 Class A, the receiver was fitted with a 10dB pad to protect the input from transients or over voltage.

I am going to place the plots side by side for both L1 and L2:


Live Terminal Plot 1 Live Terminal Plot 2

Is Plot 1 the Cheap Chinese PSU or Plot 2??

Neutral Terminal Plot 1 Neutral Terminal Plot 2

Again which one of the plots is the cheap PSU???? Yes Plot 1 for Live and Neutral terminal is the Chinese PSU!!

All measurements were made using a peak detector, looking at the plots the Chinese PSU is approximately 20+dB over the limit at its highest point and the quality PSU is 10dB below the limit giving it a Class A pass for conducted emissions.

This should give some guidance on selecting a PSU that actually does meet requirements and specifications..

By admin