There are some changes happening with how power works for marines.

1. The buildable power "packs" are being removed (they are flawed and this will help reduce stalemates).

2. Power points (on walls) are now "sockets" where power nodes must be built before the area is powered.

There's more about this in the design log (http://tinyurl.com/ns2design), but this video will give you an idea of how they look now.