Simply read the tiny text on the computer or USB power supply to see the voltage rating. Sometimes I have to take a picture and blow it up to see the text. Most laptop and USB power supplies that we have are rated for 100 to 240 volts, 50 to 60 Hz. So they take either 110 or 220 volts automatically. So in this case you don't need a voltage converter. Most electronic equipment converts the AC voltsge to something low voltage DC, so is pretty much unaffected by the hertz. A simple plug converter will work.

As mentioned earlier we also had a hair dryer with what looked like a plastic screw on the side that you would manually select the voltage. I would say be very careful about appliance voltage. It would be very easy to burn them up with either high or low voltage.

It was also mentioned that a motor seemed to run slow. An AC motor designed to operate on 60 hertz will run almost 20% slower on 50 hertz. The motor speed will be affected by the hertz. Operating a motor designed for 50 hertz will run about 20% faster on 60 hertz and the increased flow translates into more work and may overload the motor. Heating elements in a hair dryer, hot plate, or toaster aren't affected by the hertz that I am aware of. But fans and pumps do more or less work based on the speed so can be overloaded. So look for the electrical ratings on the equipment. Either UL or CE will require the label with the voltage and hertz.