So, basically, the USB port can provide up to 500mA of electric power. Given that and the standard voltage of a USB port, which is 5V, the port should be able to handle devices with power consumption up to 2.5W.
That means that most SSD disks should be supported, as during reading they consume less:
http://www.anandtech.com/show/6733/k...-v300-review/7
Hope that helps