Indeed, I seem to remember Antec make some of there PSU's like this, two fan units where the internal fan spins all the time but the outer fan only turns when the PSU gets warm under load.
I think we have to be careful here though, and check to see if the fan is seizing.
All fans regardless of how they are controlled, should spin freely, so... use the tip of a pen or other pointy device to push the fan, if it rotates freely all is OK but if there is a resistance to turning, the fan has seized up.
PSU fans can often be free'd off or the fan replaced but you have to be very aware of the potential dangers involved in "going inside" a PSU.
Even after being unplugged for several hours the capacitors within the unit can carry enough stored current to kill the weak hearted.
Sooooo be careful if that's what you end up doing.
Martin
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