I'm powering my PCB from a USB power wall wart (220VAC -> 5VDC). I believe the USB power supply (iPhone style) is a Switch Mode supply since it's not large/heavy.
When a high power motor on the same AC Circuit starts, my 5V line can vary +/-10-15V for 10-20ms. It looks more like line noise/ringing than a "square wave pull down" when I look at my scope output.
Can AC noise really affect my DC power rail that much?
I've tried putting a 10mF capacitor across 5V/Ground, but it seems to make little difference.
Are there common ways to decouple my PCB/Power Supply from my nasty neighbor?