I have had the oppsite exprence:
The cheap (~$10) chineese chargers = no interference, but you really need a 3A supply if you are going to use it with GPS on and hope to keep your device at least even on power. I bought 2 because the first one didn't use a micro usb input which meant I had to have an extra cable if I wanted to directly connect for a faster charge.
The expensive OWL charger ($50 and also not mini or micro usb) which I got for my dad as a present totally messes up the radio and only comes with a 1A charger so I'm guessing it can't keep up (never used it long enough to find out due to the radio interference and aux in hiss it generated). I contacted OWL about a fix or refund, but have yet to receive a response.