There are specifications for how those ports will behave in different power states. I suggest you just get an externally powered USB HUB. This not only offers more power than the integrated port, it will also save you headaches when combinations of items might exceed the power limit. You might think that you're not putting too much on a port, but internally, there is a "root hub", and many of those ports on the outside go to that one root hub, sharing its max output. An external HUB fixes that and it'll stay available when computer power is off.