Gelid's 1-to-4 PWM Fan Splitter allows the user to connect up to four PWM fans from just one PWM fan header on the motherboard. And because the fans are PWM the RPM of each fan will change dependent on the temperature of the CPU and/or motherboard BIOS settings, meaning the RPM and therefore noise will be reduced if the system does not demand high airflow.
The extra power required to run four fans from this splitter is provided by the 4-pin molex connector, which does need to be connected if more than one fan is used.
The cable has one PWM connector with fan speed signal wire which is connected to the first fan. The extra wire on that connector will feed back the speed of that first fan to the motherboard. The other three plugs can be used to connect three further fans but the motherboard can’t know what speed they’re running at, hence no need for the fourth wire on those plugs.