Computers require their own internal power supply because the power required to power most newer computers, especially with high-end graphics cards, would require a bulky power supply which wouldn't be ideal in transporting computers or aesthetically.
Also, with all of the other internal parts of a computer, some type of power interface would be necessary within the PC anyway, so why not just bundle it all together?
All computers have an internal power supply... An external one is simply for back up if you lose power.
It seems there is a misconception. Alternating current (AC) constantly changes direction, while direct current (DC) flows in one direction. Most electronic devices, including computers, typically require direct current for operation, but they convert AC from the mains power supply using a power adapter or internal power supply unit.
Computers
SMPS
The GameCube's power supply is internal. The whole system is very easy to transport.
it can simply be called a "power supply" or a PSU (power supply unit)
No. A UPS (Uninterruptable Power Supply) is separate to a computer which is powered electrically and contains a big internal battery for use of powering computers in the event of a power cut.
An internal power supply is usually a battery. An external power supply means the electric current that you get by plugging your device into a wall outlet. If you do not have to plug it in, then it has its own power supply inside the actual device, in other words, it is internal. Aside from a battery, it could have photovoltaic cells to generate power, or other internal sources of power, anything other than an external source.
That is a device that is inside the computer. An internal hard drive, for instance, is physically mounted inside the computer. It is not made to be used outside the computer, though there are kits to convert internal hard drives into external drives. There are external storage devices that are made to plug into a USB port. External devices either require their own power supply, or they get power from a USB socket. Internal devices get their power from the power supply which is already in the computer.
A power supply that is designed to be outside the case of the computer. Most laptop computers use an external power supply rather than an internal one to reduce size and weight while the laptop runs on battery power.
Molex and Sata
Computers are designed with functions to wake them up using local network, telephones or an internal timer. These require certain internal circuits to be powered at all times. The amount of power used is very small compared to normal operation.