I've been shopping for USB hubs for my MBP that plug into the ExpressCard slot. Nearly every one that I've found so far has a connection for an external power supply. If I'm only using the hub for 2.0 instead of 3.0, do I need the power supply?

Right now, there's a lot of hand wringing and anxiety because I don't feel I'm gaining anything if I have to lug around yet another power cord. If I don't need it for USB 2.0, then I'll feel a lot more comfortable picking one up.