Perfect example of such devices are cheap Chinese replacement chargers for just about anything. Anything that contains oscillator radiates RF and when the devic

Perfect example of such devices are cheap Chinese replacement chargers for just about anything. Anything that contains oscillator radiates RF and when the device switches relatively large currents periodically (like for example switched mode power supply) it becomes pretty good transmitter unless adequately shielded and filtered. Another significant source of EMI is almost any kind of digital sequential logic which contains signals with very sharp edges, which are mostly synchronized with each other.