The device is used with a MacBook Pro and supplied with the original transformer supplied with. I have 3 HDD 3.0 and USB 3.0 key connected permanently on. (Jéteins right decision when I cut my mac) Sometimes I self-powered devices that do not engage turn on my computer. Forced to disconnect them one by one and reconnect. This is also reflected worries with a USB 2.0 HUB Belkin home. But then I do not have any concern, the transfer is good and no disconnection. Small flat, the yellow plug serves only to load but power is not enough for my iPad 2. So I instead connect the USB key when I need to load it. But it is perfect for my iPhone 5S