Each pin in a motherboard power connector is rated for about 5-6 amps.
If the board/system might need more amps than that they do it by adding more pins/connectors/wires.
[For example. Might need more amps for some processors that fit the board but not for others.]
They added the 4-pin "P4" plug when CPU's started using more power than was available through the main ATX power connector's number of +12v pins.
The CPU power 4-pin and 8-pin are electrically the same it's just that using 8 pins vice 4 you can safely pass twice ans many amps. [Regarding CPU power connectors] It's okay to plug the 4-pin wire/connector into an 8-pin board/connector but it will only physically fit on one side of the 8-pin and so they put the guard over the side the 4-pin won't fit into.
- Power supplies built for servers might have an 8-pin and no 4-pin the so that board is simply arranged to allow you to use either kind of power supply.
Now the PCI-E power connectors. - DANGER Will Robinson!
These were stupidly implemented as they should have used a completely different plug or put them only on the actual video card.
- Some CPU connectors will physically fit - BUT! - the wires are reversed between CPU and PCI-E power.
- If you connect a CPU power wire/connector to a PCI-E board/connector (or vice versa) you will be connecting +12v PSU power to mobo ground -and- PSU ground to mobo +12v.
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The PCI-E power connectors come in 4, 6, and 8 pin versions.
Similar to 4/8 pin CPU power, the lesser pin versions fit mobo connectors with more pins.
Just don't mix PCI-E connectors with CPU power connectors and you should be fine.
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Yes, you need some kind of CPU power connector connected.
Make sure it has enough amps (enough pins) for your processor.
Don't forget that because of CPU VRM efficiency you'll need about 20% more power [watts] than the processor's TDP spec indicates.
5 amps/pin [x] 12 volts = 60 watts/pin [That's a limit, not a goal.]
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