The SSL 2/2+ is 5 volts and 500mA. That is the specification for USB 2.0 and within the specifications for USB 3.0.
It is critical that the full power of the USB port reach the interface for proper function. If you are having problems with a cable of any length try the included cable(s).
Ensure that you are plugged directly into the DAW computer and not using a USB hub for testing. USB hubs could cause power issues, or you may need a powered USB hub.
Additionally, try all USB ports on the DAW computer as some manufacturers may have USB ports that are not fully powered.