When you connect a device to a voltage higher than it’s rated supply voltage, it over-stresses the circuit inside the device. By doubling the voltage from 110 upto 220V you have also forced through much more current into the device. Chances are that 2 x voltage blew some components inside before the excess current would have over- cooked the the circuit inside. If a component has stained the board, chances are that’s what got stressed and broken down inside. The yellow stains maybe insulation from a component or transformer indicating the defect component. An electronics repair shop maybe able to help or seek out a replacement power brick? Hope this helps?