If a charger is rated at input 230 V 50 Hz and output 3V 100 mA, is given an input of 220 V, how will it affect the output charging current? Will it be lower than the rated output current or higher?
If you are talking about a cell phone charger or something like that, they are designed to maintain the output voltage for a given load and a wide range of input voltages. Most chargers don't care if they get 230V or 120V (If it is a SMPS). Further more the mains power supply has about 5-10% tolerance of the voltage as standard. So the charging current will stay the same (for a well build charger.)