Can this charger accept a three-prong head or only a two-prong head?

I only used it with U.S. / North American 2-prong cell phone charger and 2-prong laptop PC charger. It's an adapter, not a converter. The cell phone and laptop chargers actually did the voltage conversion (up to 220 volts input). I used it so I could plug my chargers into the electrical sockets in French Polynesia.