In CC071, Energy levels are not very common, especially because they are introduced very late (in Level 911). The song played in this level type is the same as the Timed song on mobile (Candy Order song on Facebook).
In T9CCS, Energy levels are introduced in Level 316 in Mango Marsh. They are a common type after their introduction, with most episodes having between 2 and 3 energy levels. Mango Marsh has 11 energy levels, which is a record for any level type in the entire game so far. Gradually, their number starts to decrease to 2 or 1 per episode as more level types are introduced.
The cake explosion acts quite literally like a cake bomb explosion.
In FCS, Energy levels are introduced in Level 751.
To win an energy level, the player must activate a specific number of cake explosions. To activate a cake explosion you must first fill up the energy level to the maximum (which changes in each level). Besides that, some levels already start with some initial energy, but most of them start with 0 energy. To fill up the energy level you must make matches in the energy tiles. After you activate a cake explosion, the energy level will go back to zero and if more cake explosions are required, you'll have to fill up the energy level again. The energy level and cake explosions act in a similar way to the sprinkleshell in Candy Crush Soda Saga. Activating a cake explosion will give you 10,000 points.
When all the cake explosions have been activated, a striped candy is made for every move remaining, giving 3,000 points for each. Then each of the striped candies activate themselves.