Fan wattage and rheobus

ok, so I have a rheobus, I put some fans on it. The fans are very low wattage, when I turn up the bus, will it deliver too much wattage for the fans to handle? or maybe the led's in the fan, Or will it simply only pull as much power as it needs, and the rest is just there? Explain what I can and can't put on the rheo bus.

As long as you don't use a fan that's too powerfull for the rheo everything will be safe, the rheo will only give it the power it needs, it won't seriously overvolt it either.