Steve,

I design power supplies and instrumentation systems. The switching power supply noise couples to your circuit through conducted and radiated energy. The 1st choice is to eliminate the noise at the source. If you have an oscilloscope you measure the amount of noise at the power supply output terminals. Use a 60 to 100 mhz scope and set the scope input sensitivity to
50 or 100mV and AC coupling, 5 uS sweep would be a good place to start.
You can also use the probe as a near field probe by connecting the scope probe ground to the probe tip. The 3" loop will show your radiated sources.

You probably will find the biggest improvement using very low esr capacitors, tantalum capacitors work well, connected to the power supply output terminals. 1kv ceramic disc capacitors connected from the output terminals to chassis gnd often helps. You need a scope to measure your improvements.

It is tough to cover everything but I hope this helps get you started.

Mark