The splitters only have all 4 pins on one of the male connectors, the rest have 3, this is normal for these cables. The motherboard can only take fan speed from 1 fan, so the cable for monitoring fan speed is only on 1 connector.
eBay
PC Fan Splitter 4 Pin PWM Fan Splitter Cable PC Case Fan Header Splitter for Computer 4 Pin or 3 Pin Cooling Fan
Aliexpress UK
1 x New Fan 4pin to 3 x 4pin/3pin extender cable 4pin to 1 Ways Y Splitter Cable 30cm/11.8". The wires are 30cm sleeved in black braiding with a 4pin female connector at 1 end and splits to 3 4pin male connectors at the other.
eBay
SATA Cooler Fan Adapter Cable，15 Pin SATA to 4 x 3 pin / 4 pin Fan Splitter Cable,15 Pin Male SATA to 3 Pin or 4 Pin Computer
Aliexpress UK
Product Function : Allows five ARGB PC fans to share a single ARGB header. Connector Type : 3-Pin ARGB connector for PC case fan lighting synchronization. Conductor Material : Tinned Copper. Conductor Specification : 17 0.12TS.
eBay
TEUCER 4-Pin Splitter Cable 4 Pin 1 to 3 Way PWM Fan Splitter Cable Sleeve Extension Braided Cable Extension Fan Connector
Aliexpress UK
IDE(4Pin) is used to connect the fan cable, and the fan connector adopts 3+1connector, which can connect the small 3Pon and 4Pin fans. Our warranty covers your machine against technical defects that develop within the warranty period defined.
eBay
SATA to 3 Pin / 4 Pin Fan Adapter 15 Pin SATA to 12V PC Case Fan Splitter Extension Power Cable Adapter
Aliexpress UK
4 pin PWM fan cable 1 to 2 way Y splitter extension. Convenient and neater solution for running multiple fans. For more than 2 fans we have 1 to 3 & 1 to 4 way cables and 5 port hubs also listed. The extension cable is braided sleeved and heat shrunk at the connectors.
eBay
PWM Fan Splitter 4pin Adapter Cable 1 To 1 2 3 4 Computer CPU Fan Splitter PC Fan Extension Power Cable Fan Cooling Y Splitter
Aliexpress UK
3 PIN PC FAN POWER SPLITTER. 1 x 3 pin connector - female. 2 x 3 pin connector - male. This cable will extend the length of an internal power cable. to stop your beloved PC from overheating!
eBay
TEUCER 4 Pin 1/2/3/4 Motherboard CPU Fan PC Case Fan Extension Adapter Cable PWM Female to 3/4 Pin Splitter Cable
Aliexpress UK
PWM 1 to 2, 3, 4, 5 fan splitter cable 26.5cm black-sleeved cable for 12V fan.
eBay
1 To 10 PWM & ARGB Hub Splitter SATA Powered 4 Pin PWM 3 Pin Addressable ARGB Adapter ARGB Controller Splitter for PC Case Fan
Aliexpress UK
4 Pin PWM 3-Way Fan Cable Splitter. Allows for three 4-pin fan connectors to use a single header. We'll always aim to respond as quickly as possible, usually under 24 hours.
eBay
JEYI 1 to 3 ARGB Splitter Cable, 5V 3Pin Addressable RGB Extension Cable with 3 Pin Female Connector, for 3-pin ARGB Sync PC Fan
Aliexpress UK