Ordinary "wall wart" or "pulsed phased" or "switching" voltage transformers are typically very dirty and contribute greatly to contamination to your power supply. This is a recent phenomena. Over the last 15 years they have proliferated with mobile phones and computers in sequence for charging and powering.
The old fashioned ones were safe as they used 2 copper coils. With micro chips came switching and this causes SPARKING that creates a powerful burst of radio frequencies many times a second. LISTEN TO YOURS WITH A RADIO on the AM band at ALL frequencies. Some are better than others but all are bad as that burst goes down the wires as well.
As Stalin said you can leave the West to EMR poison its self out of existence. Most of these are coming from China now. There are nearly no clean alternatives available now. Those that are available are very expensive. IE magnetic voltage transformers. Look for linear power supplies (regulated) or linear mag amps.
If you are EHS you most certainly should be powering all your devices with linear 12vDC power and 5vDC. IE TVs computers etc.
If you are interested in all this read Electromagnetic Man by Cyril Smith. He discuses these 50 and 60Hz issues and explains risks and effects.
If you need a clear DC source for charging your USB devises I have just found one cheap on eBay.
LT1083CP Linear Voltage Adjustable Regulated Power Supply Module Board
My radio did not pick up any dirty radio emissions. This does need a bit of wiring up but it is worth it. Especially for charging batteries, it would be well handy, as I have never found a clean battery charger.
Does any one else have experiences with clean 12vDC?