Modern motherboards have two power connections. The large main connection has either 20 or 24 pins. The smaller connection has either 4 or 8 pins.
Do you mean you have a pc with a Pentium III cpu? I built a pc at least 10 years ago with a Pentium III 500Mhz cpu. Or was it a Pentium II? I am growing old disgracefully and I forget things. I can't remember if the motherboards back then had a second smaller power connection like modern boards do. I don't think they did. I wonder if that's what leo2kp meant?