No, they are sort of similar though. They are both 19" FD Trinitron monitors, but the Sony G400 also has extra features like dual inputs, so you can hook up 2 computers to the same G400(there is a little switch on the front to change between input 1 and 2). The 21" version of the monitor from Dell, the P1110, does have the dual inputs.
The monitor I have, the IBM P96 is also similar to those two. It is also an 19" FD Trinitron monitor and also has the dual inputs like the G400. I picked the IBM over the Sony, because I wanted a black monitor, although I think Dell also has a black version of the P991, but I think you have to buy a Dell Dimension 8100 computer to get it in black.