The components inside the box may be charged with extremely high voltages, and may injure or kill you. If not, the box may be broken, and you will need to buy a new one. It is safe to open one, if it hasn't been connected to any power source for a while (>1 week), however, I still wouldn't recommend it.
Power supplies are rated at the maximum wattage they can put out. Of course, a computers requirements vary depending on what the computer is doing, so a computer power supply should be of the same, or greater, wattage requirement of the computer when under it's greatest load.
ATX
Computers work on DC supplies and convert AC to DC supply through SMPS (fixed in cabinet). Specifications of SMPS decides the load a Computer can handle.
It is a switching regulator.
If magnets and electromagnets were never invented, it is likely computers would not exist. The first computers required the magnetic properties of relays and/or vacuum tubes to function. Even modern computers rely on magnetics to spin fans, spin hard drives, CD/DVD drives, produce sound, provide power through the power supply, increase voltage through induction, rectify power flow, and read/write data to hard drives, floppy drives, and other magnetic media.
Computers
SMPS
it can simply be called a "power supply" or a PSU (power supply unit)
Molex and Sata
A computers power supply can cause a shock even when unplugged but it's not dangerous. The monitor stores enough power to kill for many years after being unplugged. Never open the case of a monitor.
TRUE
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?
-Power Supply Unit. -Monitor.
The first power supply was invented by Thomas Edison. It is unknown when exactly the first universal power supply for computers was invented.
Power supplies are rated at the maximum wattage they can put out. Of course, a computers requirements vary depending on what the computer is doing, so a computer power supply should be of the same, or greater, wattage requirement of the computer when under it's greatest load.
All computers have an internal power supply... An external one is simply for back up if you lose power.
any power supply with at least 175 watts