If the card will fit in the box it'll probably work for you. When I looked up Dell Vostro 200 they were built into two kinds of cases. There was one type built in a slim case and the other type built in a mini case. The mini case is much wider than the slim case. It looks like both types of cases sport motherboards with X16 PCI-E slots for adding an aftermarket video card. Trouble will arise if your 9550/X1050 video card has an AGP connector instead of a PCI-E connector, or you have a full size video card and a slim case.
It appears you need an AGP low profile card for the slim type case. Since you already have the graphics card, is the rear I/O plate short enough to fit? If so, it is a low profile card. If not, the card is built for a standard width case and you can't use it with your slim case.