所有電腦的USB都有5V輸出，標準輸出電流的0.5A, 如果USB divice 需要大過0.5A,當然要買自帶電源的。

要還是不要，要看你的 divice 需要的電流。一般的外接 divice 如果·超過0.5A. 都會自帶 power supply 。例如外接的硬盤，特別是機械式硬盤。

 

What is the power output from a computer USB port? Most computer USB ports supply 5V of electricity with a maximum current of 0.5A. This amount of current is standard across the majority of computers and means the overall power output will be 2.5 Watts at best. Later USB designs bring that current up to 0.9A.