The power cube is an object that appears in the Sonic the Hedgehog series. It is a device that can be used to open sealed doors or paths by placing them into their matching fixtures, similar to Key Stones.
The power cubes look like rectangular cuboids made of glass, with two opposing square-shaped sides made of metal, and have each a piece of machinery inside them that can be seen through the glass. They all come in four different colors: purple, yellow, blue and orange.
In Sonic Adventure, and its enhanced port Sonic Adventure DX: Director's Cut, power cubes appear exclusively at two points in Amy's version of Hot Shelter: first in a room filled with monitors where the power cubes lie in plain view and later at the end of the Action Stage, where some power cubes are hidden and ZERO is harassing the player while Amy tries to use them. The power cubes always appear in sets of four, each of them in a different color.
Power cubes are used to unlock blocked paths and doors within Hot Shelter. To unlock them, the player has to pick up each of the power cubes in the area and put them into a nearby fixture that matches the power cube's color. Once all four power cubes are inserted, the path/door will be unlocked. If a power cube is inserted into a non-matching fixture, nothing will happen. However, if inserted or just placed in the proximity of a matching fixture, the power cube will automatically insert itself.