Freeagent portable drive gets port surge message

USB ports have a max current requirement. A new device can exceed
that current for a limited time. USB ports must have a filter so that
excess current does not create the alarm condition.

So either your flash drive exceeded that current requirement or your USB hardware is marginal - gets tripped by a current that is not so
excessive. Often components used in that filter have a 10% error
margin.

You should see the error in the event viewer.