No that isn't really the case, Switchers are troublesome when it comes to noise especially the Mains type switchers however a small choke and a couple of good 10 to 47 uF caps will contain that rather nicely. the other thing to consider is that all the little ones based on the LM2596/75-6 type devices operate at 50 Khz and many if not all of the new ones operate at considerably higher frequencies 150 KHz to 1 - 2 Mhz is common now. This is considerably higher than the Arduino is "Likely" to be able to detect and produces little interaction. All four of the devices I own have noise levels < 100 mV at 5V DC out. The Final point is if you can reduce your power supply demands you can reduce your power supply size or increase the available load current by the gain in efficiency. There is also another point here and that is simply to power the non critical heavy current loads from the switcher. Your information was very correct 15 20 years ago but times have changed considerably. I'm about as "Old School" as anyone around but with an understanding of the devices and their applications they are great tools. Linears? yeah sure... for critical low noise LOW CURRENT applications only and even then I personally would try one and very carefully analyze it before discarding the idea... They'res just too much to win by choosing a switcher.
IMO
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