I didn't think anyone still listened to AM radio apart from Radio Hams and those of the religious persuasion.
What I would try is an in-line Mains filter, that your radio plugs into and then the filter plugs into the wall.
AM radio suffers with computers, because of the internal ferrite aerial rod and the fact that computers have so many harmonics that occur in the AM Broadcast band.
One other thing you shouldn't forget is the fact that radios are built to a price these days and have been for some years, any sort of RFI rejection circuitry, is usually the first thing to be tossed out of the formula, in the name of "affordability".
