These are called CLASS II devices and they are designed with double or reinforced insulation. In plain terms it means that the current carrying components are themselves insulated AND surrounded by a second layer of insulation. That or the current carrying components are protected by reinforced insulation like a hard plastic case.
A practical example is the humble power brick or wall wart. These are class II power supplies which are enclosed in a hard plastic case which protects the user from electrical shock.
