A simple ferrite ring filter (OD = 1.14", ID = .748") installed on the DC power cable of a wall wart power supply can help suppress the noise interference to nearby electronic devices by suppressing the fundamental switching frequency (usually under 1 MHz) and thereby suppressing harmonics at higher frequencies. This kit includes 100 filters useful for all types of devices powered by wall wart power supplies including laptop computer, routers, cable modems, wireless phone charges, USB chargers, etc.