Determination circuit of power adapter

The present invention relates to a determination circuit of power adapter, which includes a fixed resistor, a fixed power supply, a determination unit and an identification resistor. The identification resistor is disposed in a power adapter of a portable apparatus; the power adapter with different output power is equipped with the identification resistor with different resistance; the fixed resistor, the fixed power supply and the determination unit are disposed in the portable apparatus; the fixed power supply is coupled to the fixed resistor and the fixed resistor and the determination unit are mutually coupled; when the power adapter is inserted in the portable apparatus to supply power, the identification resistor is also electrically connected with the fixed resistor to generate an identification signal and transmit the signal to the determination unit so as to determine the output power specification of the power adapter in accordance with the identification signal.