3-pin DC fan connectors are connected to the motherboard, so you can alter its speed by limiting the voltage via BIOS.

They cannot be manually controlled but can only be limited using a resistor cable.

Molex fan connectors take power from the PSU.

From left to right: A 3-pin connector, a 4-pin connector, and a MOLEX connector. You can also check the end of the fan cable to know if you can control the fan speed on the PC. You can control only those fans that are connected to your PC motherboard but if these are connected to the power supply then you can’t manually adjust their speed. The method to control the fan speed on a laptop and PC is highly dependent upon how your PC fans are powered. What type of CPU fan you can control on PC? The problem only starts when you constantly hear CPU fan noise or nothing at all when running tasks. It doesn’t matter if it’s a high-end gaming rig or gaming laptop you will hear a CPU fan noise when you boot up your PC and sooner the startup process completes the noise goes on to decline. While running multiple applications on Windows OS or tabs on chrome you might feel hot air coming out of your system. Every PC and laptop has built-in fans that blow off the heat generated when a process is running through.

Msi fan speed control