The present invention provides a power converter, a secondary side controller, and a short circuit determination method for a current sensing resistor of the power converter. The power converter is controlled by a power switch to convert an input voltage to an output voltage, and provide an output current to an output terminal. The power converter senses the output current by a current sensing resistor to generate first information which relates to the output current. The power converter generates second information according to an ON time, an OFF time or a switching period of the power switch, or according to an energy-releasing period for transmitting energy to the output terminal, wherein the second information indicates whether there is a substantial amount of energy transmitted to the output terminal. By checking whether the first information and the second information are contradictory to each other, a malfunction can be found.