Hi Leon,
No Problem. Another (perhaps quicker
) way to tell before you spend your money on unwanted cables or adaptors is to check in the specification section of the monitor manual or on Dell's website.
The connection specification online or in the manual will say DVI-I or DVI-D.
If the monitor connection spec in either of these say DVI-D then you will need the electronic analogue to digital converter and cable.
If they say DVI-I you will only need the cable/adaptor and not the elctronic convertor.
Cheers