You may find this kind of supply in audio amplifiers, computers, tape decks, and other equipment
. This image shows noise from my computer, most of which is from the power supply. To get this image, I had to remove the side of the computer case, and move the rabbit ear close to the computer. The sparkles are probably individual switch pulses, and the fine weave is probably other computer stuff.
My computer spews signal every 40 kHz, multiples of the switch frequency. The computer jams a local AM station station, on 1080 KHz, 200 meters up the road from my house, even though this 10 kW AM station transmits from a tower only 5 kilometers meters from my home. A couple of power strips and some grounding helped with that.
To cure this sort of interference, you can turn off the device, or arrange it that you have more distance between the device and your antenna.