Power plant diversified for the Second Tiberium War. Nod had a normal nuclear power plant, whereas GDI had a power plant that could be upgraded with power turbines to increase its output. However, Nod could build advanced power plants which, at the expense of space, could produce much more power than the normal power plant could.
Third Tiberium War
In the Third Tiberium War, both sides upgraded the designs which varied greatly. GDI moved on to utilise plants that generated clean, efficient power and could be upgraded with advanced power turbines, similar in design to those from the Second Tiberium War while Nod decided to use plants that generated power from Tiberium and could be upgraded with liquid Tiberium cores.
Both the GDI and Nod have some power consuming buildings, such as Technology Centers and, for Nod, Obelisk of Light, while GDI had the Sonic emitter. If a base ever runs out of power, certain buildings will not function, and units would be produced more slowly. However, there is the option from the Second Tiberium War and beyond for commanders to shut off certain power consuming structures, thereby saving electricity until more power plants may be constructed. The Scrin, who invaded Earth in the latter half of the Third Tiberium War, also have their own power plant, called reactor, which runs on Tiberium and can be upgraded with fusion reactors.