Voltage adjustment system and method thereof

This invention discloses a voltage adjustment system and method thereof. The voltage adjustment system comprises a voltage adjuster, a first power unit, and a second power unit. The voltage adjuster is electrically connected to the first power unit and the second power unit. The first power unit transmits a first power having a reference voltage to a host of a portable apparatus to be a working power. The second power unit transmits a second power to the voltage adjuster. The voltage adjuster adjusts the second power to be the working power based on the reference voltage and then transmits the working power to the host. By way of the mentioned above, the first power unit and the second power unit can provide powers to the portable apparatus simultaneously.