Fan slows down when miners are connected? Miners aren't able to run full speed?
Probably your hub is underpowered.
Yepp the miners it must be the problem that orico is not good enugh anymore. But power a fan with USB is always slow.
But i found something interesting on Amazon Icstation Boost Converter MT3608 Mico USB DC 2V-24V to 5V-28V 2A , Voltage Regulator,Power Supply Step Up Module 3.3V 5V 6V 9V 12V to 5V 6V 9V 12V 24V this should work. found it on this video
https://www.youtube.com/watch?v=I6xlSUBCkhA