Hi Sir,
We provide 5V, 2A standard adaptor as default and I use it in my test with only keyboard inserted, no other usb devices loade, It is working fine.
If you need to use more USB devices, please choose a USB HUB with external power supply source or stronger adaptor (5v, 3a or above).
When using USB harddrive, it is better to use a HUB with power source, the output of USB on board is 500ma in MAX, not enough to drive the harddisk.