How can I avoid distorted analog outputs?

Especially when clocked power supplies are tested, situations may occur in which the monitor outputs for current, voltage etc. at the analog I/O connector are distorted.
The causation has to be searched in the way of test assembly.
Clocked power supplies have got filters in the output circuit and capacitors from the output to protective earth.
Also the electronic load and other instruments include filters because of EMV reasons.
The common mode noise voltage (voltage between each output terminal and protective earth) causes a differential current through the anti-interference capacitor and the electronic load (or other instruments) back to the load output.
This differential current often generates high-frequent superpositions at the measurement signals.
At dynamic tests very high interference voltage may occur.
To solve this problem, you can supply the electronic load and/or the other instruments by insulating transformers with low coupling capacity.
Thereby the interference circuit is interrupted and the measurement quality is increased.