Just bought an Acer C120 Projector. It comes with a separate power adaptor, ( comes with a 2 pin plug and a 3 pin plug) the 2 pin plug fits in perfectly, but...............the 3 pin plastic plug does not fit in the hole ! where am I going wrong ?, does anyone else have this model? Please can you help ? it works ok just using the USB connection, but I've read that using the extermal power supply boosts the brightness. Thanks in advance.