Here's how fan speed reading works. Most fans generate a speed signal (2 pulses per fan revolution) and send to back to the mobo header on Pin #3 of the header. The mobo circuitry then counts those pulses to display a speed for you, whatever tool you use to display them. Some first of all, the ONLY things that can count speeds for display are the mobo headers (well, excepting some added special circuits in certain AIO liquid CPU cooler systems). So any fan plugged into a power output directly from a PSU will never show you a speed becasue4 the PSU has no way of dealing with the signal.
Secondly, a mobo fan header can only deal with ONE string of pulses coming in from a SINGLE fan. So, if you use a Splitter or a Hub to connect more than one fan to a particular header, that device will only send to the header ONE of the fans' speed signal pulses. It simply will not pass speed signals from any other fan to anywhere, so the other fans' speeds all are invisible.
So, you can only "see" ONE fan speed on each MOBO Fan header. No extras, and none at all if they are connected directly to the PSU.
Third-party add-on Fan Controller modules that you mount in the front of your case and use to control fans manually often also will show you the speed of each fan they handle. But that info is not sent out anywhere else, so Speedfan will never even know such info exists.