I have perhaps a dozen PT switchers, but they're not "little" (<2.5 Amps) or they don't perform adequately. I have received some samples, doncha know!

Apparently you mostly use DC-DC converters. That's probably because you design displays for mass transit vehicles.

I've tried a few of those small converters along with wall-warts but I've never seen one hold an adequate noise limit. I require less than 0.1% of Vout (5 mV at Vcc=5 volts) as noise at 10% rated load and 1.0% of rated output at 90% of rated output (50 mV at Vcc=5 volts), as tested with a static load resistor. There are, of course, other constraints.

RE