I have a few 12V wallplug PSUs which plugs into the wall AC mains socket, and it gives out 12V DC.
When they are used for the other devices, they are perfect - powering them and making them work.
But when they are plugged into my Shortwave HF Receivers, they are the source of the hash noise in the receiver.
It is very high level of static noise they cause, so that the receivers are not able to hear the weak signals.
Are there known effective ways to clear this problem? Obviously these wall plug DC PSUs are not the radio's original PSUs, but they are the cheaper OEM made or unknown makes.