A USB hub is a device that lets you plug multiple USB peripherals into one USB port. You plug the hub into a port on your PC/PS3, and it has several USB ports that you can plug devices into.

A powered USB hub is one that includes a power cable, so that it's able to provide power to every device instead of drawing power from the PC/PS3's USB port. USB ports do not provide metric tons of power, so if you're plugging multiple power-hungry devices into one, they won't necessarily work.

Have you tried using the adapter on your PS3 with just the keyboard plugged in instead of both keyboard and mouse? If it is a power issue, taking out the mouse might provide the keyboard with enough power through the PS3's ports.