You can try a simple line filter first but that isn't likely to work with the type of noise common on AC lines today. Schaffner makes some excellent high performance line noise filters but they are designed to be chassis mounted, the simple plug in type filters like you may in retail stores are simple and tend to not be terribly effective.
Isolation transformers often are very effective because of their shielding and some plug and play units are available but not many are available in the low power size that you need so you may have difficulty finding a unit that isn't excessively costly, large, and heavy. Avoid the "autoformer" types that are often found on Ebay and the big online shopping types which aren't a real isolation transformer but instead are a simple tapped auto transformer designed to cheaply convert between 240/120 supplies and 120/240 volt products. These offer zero attenuation of noise on the line.
Mouser Electronics is where I have bought most industrial electronic components for years and they have these products but they are NOT simple plug in devices and you would have to mount them to a chassis and wire in the proper three wire power plug (with proper circuit breaker or fuse) and an AC outlet. If you go this route, Schaffner offers excellent filter modules but they aren't cheap AND there is no guarantee that it will work. So first see if Best Buy or some online source has an inexpensive plug in filter and give it a try.
If you go with the battery inverter route, look for something that is referred to as a true or pure sinewave inverter because these provide the cleanest output and the best provide a waveform that is nearly a pure sinewave. So called "modified" sinewave inverters produce a dirty output that won't kill most electronics but the output is a slightly softened square wave rich in harmonics and other "garbage".
Rodger
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