Converting a DeWalt charger from 110V to 220V, rational of component selection from the guide
It's all in the comments already. A risky business and can cause bigger damage than you expect. Think about a fire when you are sleeping. Without a schematic and proper research its detailed operation it's impossible to decide how near to blow the charger really is after making those changes.
I have seen chargers that operate as well with 110V and 240V and both 50 and 60Hz. They are designed for that range. Larger margins require more complex design and higher cost parts. It's very difficult to believe that mass produced equipment suppliers want to carry that extra cost overburden.
Where I live modifications like this would be considered criminal, because there still reads all original supplier's texts and the device is changed to other. In addition only a contractor who has the licence determined by the regulation code can legally make works which change the structure of mains AC operated equipment.
Not asked: The white glue mass is essential to keep the device at least some time as one piece when it's transported in a toolbox in a car. Soldering joints alone will not stand vibrations of big parts. The ceramic resistors need it as well as the capacitor.