I'm learning on Arduino and wonder something about external power supply.

1) My board is Arduino Uno and usually connect to my computer through the USB cable, can I use an AC power adapter that can be connected through USB port? Is it possible or fine to do this?

AC power adapter <-> USB port <-(USB cable)-> Arduino port ( I don't know the name... )

2) What kinds of components can be used as external power supply for Arduino board? It's really nice if you have some images or names about them.

Really appreciate your support.