Ah, so you wouldn’t generally have large enough capacitors without crazy expense to handle transient voltage drops throughout the home, you’d at most do EMI/RFI filtering. Or add some kind of UPS with the power to handle a second or two of voltage sag.
Not sure it’s noise in the line or not, not sure where it’s coming from. My theory was voltage sag, but then again I’ve got an AC->DC in there to get the 12v. So I’d have figured it’d handle “low” voltage fine from the 110v, just pull a few milli-amp more as part of the process. Whereas noise…yeah, noise could possibly getting through.
I’m not too familiar with these sorts of electronics bits at all. Just take a electrolytic capacitor and stick it on V+?