An external 3.5” mechanical hard drive would definitely need a separate power source. An external 2.5" USB 2.0 drive usually needs an external power source though I've seen them work without one. The power available on the USB port is one deciding factor. Some devices provide more USB power than others and some drives and cases require more power than others. A USB Y cable to draw extra power from a second USB port can help. The 830 would need two USB ports for that though.