These clip on cores are powerful enough.

eBoot 20 Pieces Clip-on Ferrite Ring Core RFI EMI Noise Suppressor Cable Clip for 3mm/ 5mm/ 7mm/ 9mm/ 13mm Diameter Cable, Black

If you have a cord with a driver of fluctuations at end A and device at end B and your concern is the flux coming off the wire, then you want to place the core close to the driver. The effect is to smooth out most of the undesirable oscillations on the down stream side. It doesn’t have as much of an effect on the upstream side.