I have a Yamaha - DGX 505 , but the normal USB sticks does not fit. Is there any adaptor, that I can use? The normal USB are much broader than the connection at the back allows.
The USB port at the back of your piano is not for a USB drive, but it is for connection your piano to a computer as a usb device. If you need to use Midis on your piano, try copying them to a smartMedia card, which can be used in the front slot.