Extent of ground plane beneath filtered DC converter?
That round Siemens inductor will have lots of external field lines, because there is no closed path. The air path is 1cm or 2cm (10mm or 20mm)

The cheapo switcher inductor looks like a black tub with central core, and the flux only has 1mm or 2mm air path, thus much less external flux to be a bother.

That round Siemens inductor will induce voltages (Faraday Law induction) all around on the PCB.

Find a closed-ferrite-path inductor to use.