Secondary controller applied to a secondary side of a power converter and operation method thereof

An operation method of a secondary controller applied to a secondary side of a power converter, wherein the secondary controller comprises a detector, a standby signal generation circuit, and a comparator, the operation method comprising:

• the detector detecting a first signal and a second signal of a universal serial bus device and a frequency of a synchronization signal corresponding to a primary side of the power converter;
• and
• the standby signal generation circuit delaying a first predetermined time to generate a standby signal to a primary controller of the primary side of the power converter when the detector fails to detect the first signal and the second signal, and the frequency of the synchronization signal is less than a first predetermined frequency, wherein the primary controller enters a standby mode according to the standby signal.