The invention discloses a power transformer. The power transformer comprises a shell, a detection module and a transformer main body; the detection module is arranged in a chamber of the shell, and is provided with a converting unit and a judgment warning unit; the converting unit is capable of automatically identifying an input voltage and sending out a voltage converting instruction; according to an output voltage, the judgment warning unit performs a high-frequency flashing alarm if the judgment warning unit judges an overvoltage of the input voltage occurs, or performs a low-frequency flashing alarm if the judgment warning unit judges an under voltage of the input voltage occurs; the transformer main body is arranged in the chamber of the shell to have an electricity or signal connection with the detection module, and is used for executing the converting instrument sent by the converting unit, so as to convert the voltage. The power transformer identifies and judges the input voltage through the detection module connected with the transformer main body, so as to automatically and intelligently convert the high voltage and the low voltage of the power transformer, so that electric appliances are suitable for domestic and overseas voltage standards; and moreover, the detection module performs the high-frequency flashing alarm if the overvoltage of the input voltage occurs, or performs a low-frequency flashing alarm if the under voltage of the input voltage occurs, so that a user can timely find whether the input voltage of the power transformer is the standard rated input voltage of the power transformer or not.