SMPS noise suppression
The classic 'clip-on' ferrite is intended simply for the power cable to pass through once with the hole diameter ~equal to the cable diameter.
If you're able to pass the cable through more than once, there's an advantage since the effectiveness of the filter ~~proportional to the number of 'turns'. If you can pass the cable through multiple times, so much the better ! There's no 'loading effect' at 50/60 Hz to concern yourself with as the ferrite only has meaningful effect at radio frequencies.
Ferrites designed for this application are a bit different to the ferrites used in switch-mode transformers etc. They are 'lossy' and convert some energy into heat. This makes them more effective at suppressing interference than an inductor alone.
You might like to investigate ferrite ring cores that allow you to wind many turns on them if you're having trouble reducing your EMC problem.
It's not asked but you may also get some benefit from a ferrite on the DC output cable too.
Some more info is available here .....
https://en.wikipedia.org/wiki/Ferrite_bead#:~:text=A%20ferrite%20bead%20%28also%20known%20as%20a%20ferrite,ferrite%20ceramic%20to%20build%20high-frequency%20noise%20suppression%20devices.