12v power supply design

Are you using a ferrite core on the power rails?

Yes, and im going to experiment with c’s

Yes, and im going to experiment with c's as well

Given the power level you’re monitoring I don’t think a swmode psu will make the slightest difference.

I’ve used swmode psus powering thermocouple amplifiers with 40uV/C input controlling kW of load with no problems

perhaps you could post an accurate schematic and layout of your project and we may be able to help you

regards

Allan