Many kinds of electronic equipment use an external brick power supply unit. There are several advantages to this; it keeps heat and noise out of the product, and it reduces the scope of electrical safety considerations, as discussed in What's the reason to make power supplies external?
Nonetheless, despite early home computers tending to use external bricks, desktop PCs soon settled on internal power supply units. Why? What's the advantage of an internal unit that outweighs the disadvantages?