A data transfer apparatus (“DTA”) connects to the field generator in a TTFields therapy system using the same connector on the field generator that is used to connect a transducer interface to the field generator. The field generator automatically determines whether the transducer interface or the DTA is connected to it. When the transducer interface is connected to the field generator, the field generator operates to deliver TTFields therapy to a patient. On the other hand, when the DTA is connected to the field generator, the field generator transfers patient-treatment data to the DTA, and the DTA accepts the data from the field generator. After the field generator and the DTA have been disconnected, the DTA transmits the data to a remote server, e.g., via the Internet or via cellular data transmission.