IF I understand the OP's question correctly...
Does a USB charger output different voltage based on input voltage?
Short answer is NO, USB Standards world wide is 5 volt DC @ 500–900 mA (roughly). So the real question is, can the charger take 90-250 volts AC and convert it to 5 volts DC with out frying it self?
In other words, you should be fine plugging in your USB devices!