An AC Adapter is a cord used to charge handheld systems or power consoles. All Nintendo consoles come with AC adapters in the box, but the first handheld Nintendo system to include one was the Game Boy Advance SP, although there were optional adapters for older systems, which usually also included a special battery that could be recharged.
The Game Boy Advance SP's adapter was black, rounded, and had a wide plug. The Nintendo DS's adapter was dark gray, still rounded, and had a small, flat plug. The Nintendo DSi and Nintendo 3DS's adapter is light gray, more square, and has a somewhat rectangular plug.