How to cure SMPS output to get upset by a switching device
SMPS as a unit has high bandwidth therefore any not filtered high frequency signal at its input will appear at its output. DC-DC linear chips are also have the same frequency response and any high frequency signal at their input could be appeared at their output.
just in case that you are using isolated transformer with iron core for an AC-DC convertor you have an intrinsically filter for some high frequency signals.

If you cascade proper Common Mode Filter at the DC/AC input and then proper low pass differential mode filter at the SMPS input, you could be sure about bypassing the injected noise at the input of SMPS from its output.
Remember for measurement such phenomena it is recommended to use probes in their X10 mode and do not use their attached long 3-4 inch Ground cable. you have to use the very short ground clips that is companion with probe's purchased package.

Ringing is also companion with an SMPS that is not implemented with good PCB. Please look at the related TI document (SLPA005).
In addition to conducted emission the Grinder has strong radiated emission too.
using proper casing and filter (Common mode) at the input and output of the SMPS could be helpful.
Please look at the following links:
https://www.giee.org/wp-content/uploads/2016/08/ferrite_bead_181_hex_open_and_closed.jpg

https://www.radiodan.com/Henry/parts/RF_chokes.htm