No, there are different kinds of PSUs. The most common ones today are ATX PSUs with a 20-pin ATX connector that goes to the motherboard. However, there are older style motherboards without the 20-pin ATX connector. Also, P4 motherboards have another connector (I don't know what it's called). New motherboards with PCI-e slots have a 24-pin ATX connector to supply the PCI-e slot with the needed extra power.