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Ok, let's try and reason out this rather unique question. Firstly, the CPU is a flat lil chip with around 700-1400 pins underneath, depending on which model you have. Where in the world would you find a connection to transform your mains AC power into those pins? And furthermore, how would you get the computer to communicate with the rest of the computer if it's plugged into the mains?
Ok, so let's move onto the motherboard. The motherboard has the socket for the pins and the power phasing circuitry to keep steady voltages supplied to the CPU. Would you then try to plug that into the mains? Most motherboards have 2 power connectors - a long 20+4 pin 12V ATX power socket and a small 4/8 pin ATX power connector located right next to the VRMs on the motherboard (I forget if it's a 12V connector or less). There is no way you can directly plug 220V AC power into the motherboard without something blowing up, it needs 12V, not 220V.
Ok, so let's get the PSU back into the picture. It transforms your 220V AC power from the mains into much smaller direct currents across it's rails. 12V ATX power for the motherboard, 5V power for USB and lesser components, and another 12V for PCIe power if it's a modern power supply. It completes th system. It's necessary. And if you get the cheapest PSU possible, that's like getting the cheapest fuel possible for a car from an unlabelled canister from some shady guy down an alley. There's a very good chance of something blowing up.
Monitors are external to the PC, and require AC power from the mains just like a TV. Some PSUs feature an AC out port for you to plug a monitor in, or even some speakers. I've not seen any modern PSUs with that feature though. The only other parts that require power from the mains are external devices like printers, scanners, external drives and a certain expensive logitech keyboard, the G19. Everything inside the computer gets it's power from the PSU.
Ok, so let's move onto the motherboard. The motherboard has the socket for the pins and the power phasing circuitry to keep steady voltages supplied to the CPU. Would you then try to plug that into the mains? Most motherboards have 2 power connectors - a long 20+4 pin 12V ATX power socket and a small 4/8 pin ATX power connector located right next to the VRMs on the motherboard (I forget if it's a 12V connector or less). There is no way you can directly plug 220V AC power into the motherboard without something blowing up, it needs 12V, not 220V.
Ok, so let's get the PSU back into the picture. It transforms your 220V AC power from the mains into much smaller direct currents across it's rails. 12V ATX power for the motherboard, 5V power for USB and lesser components, and another 12V for PCIe power if it's a modern power supply. It completes th system. It's necessary. And if you get the cheapest PSU possible, that's like getting the cheapest fuel possible for a car from an unlabelled canister from some shady guy down an alley. There's a very good chance of something blowing up.
Monitors are external to the PC, and require AC power from the mains just like a TV. Some PSUs feature an AC out port for you to plug a monitor in, or even some speakers. I've not seen any modern PSUs with that feature though. The only other parts that require power from the mains are external devices like printers, scanners, external drives and a certain expensive logitech keyboard, the G19. Everything inside the computer gets it's power from the PSU.








