Matty, the power requirements depend on the model of laptop. They are different even among different models of inspiron and latitude. Even if the connector is the same shape (they are for the most part, but in a few instances they are not), sometimes the bios gives you a warning that the power adaptor is not compatible, or won't let you boot up at all. I have used power cords that don't match exactly to the laptop, but I don't know if I would recommend it.
Having said that, I think most Dell cords should give you juice to the laptop even if they don't match exactly. It's possible it could fry your battery though.