Thanks for the replies. So when rule 12.51 says
"Units may trace supply from an enemy controlled Area at no additional cost. However, units may not trace supply through or into an enemy controlled Area."
does it mean that any depot placed in an enemy controlled area can only supply units in that area?
Otherwise I am having a hard time understanding why this rule doesn't make supplying SME impossible because it seems like I am trying to trace supply into SME, which is enemy controlled.
12.5 and 12.51 are two different -- but similar! -- things and often confused. 12.5 is the supply line a unit uses to receive supply, and trace back to a supply source for VP purposes. 12.51 is the path a depot follows after it is placed on the board at a supply source. Depot route tracing is something you don't actually "do" in practice when you're playing -- it becomes second nature. But for learning purposes, follow along with 12.51 and actually start the depot on a beach (Allies) or in a Zone (Germans) and trace the path the depot can legally follow before it stops.
From wherever it's placed, then the supply lines emanate from there and you use the point values listed in 12.51 for the refit cost.
As an example of the difference between 12.5 and 12.51: A supply line
can pass through a contested area that your side controls (at the cost of an extra point). A depot
may never pass through a contested area on its placement route.
*And just to make things a little gnarlier, the only contested areas a depot can be placed are on the Allied beaches -- and that's because they're the Allied supply sources
To your specific SME example: The depot is placed on Utah. It can't travel any farther because SME is contested. You can supply into SME because you own the bridge on a flooded boundary. Units on Utah cost 1 (spent) or 2 (disrupted). Units in SME cost 2 (spent) or 3 (disrupted). You count SME as a .1 contested VP because you can trace a supply line back to a supply source as a result of owning the bridge on a flooded boundary.
Keep asking any and all questions. In practice, the rules aren't very hard. But they give nearly everyone problems who try to learn without a guide. And keep pushing through the learning pain. It's such a fabulous game with an even better community behind it.