If it were really a transformer with one primary and two secondaries the "in" and "outs" wouldn't matter and it would indeed be a "T" or splice. Ain't no such thing.
Anyway, answer your own question. Take a 2 way splitter and connect a cable drop to an "out" and a TV to the other "out". What do you get? Now connect the TV to the "in".
So, it passes a signal from the "in" to the "outs" and vice versa but not between the "outs".
This will hold true for any splitter configuration and if you want it to work observe the in port.
-Hal
