I have 2 arduinos connected using I2C on the analog 4+5. I would like to have them powered separately. However if I just plug in 2 AC adapters, the communication between both devices stops working. The two adapters are different brands, but they have the same voltage rating and polarity on the casing.
I have a feeling I'm dealing with a very basic electrical engineering principle here, but I don't get it :-?