Methods of and apparatuses for characterizing the power supplying capabilities of host power supplies providing power to wireless modems. According to an exemplary method, an equivalent series resistance of the power supply is determined and compared to a plurality of maximum equivalent series resistance values associated with a corresponding plurality of transmission power classes. Each power class is designated as a permissible power class at which the wireless modem may be configured to transmit, for each maximum equivalent series resistance value that is greater than the equivalent series resistance of the power supply.