only use one usb cable no need for a power cord or you can power it from an ac ... enjoy bigger better sound nx-u10 usb powered stereo speaker how does it work ... powerstoragetm circuit if music varies in loudness or ... its signal level is not constant the power used to play music is an average of ... is supplied the remaining 7/8 of the power is unused the powerstorage circuit max ... instantaneous power 20w stores this unused electric power ... and peak required power supplies only enough to unused power ... match the music level stored power maximum power this high efficiency ... supplied by usb 2.5w powerstorage circuit can achieve 20w output even ... with the small quantity of power time powerstoragetm circuit conventional usb speaker ...