Dew heater with ASIAir

I have a generic, 5V USB dew heater from Agena, and I bought USB to 12V adapter so I can connect to my ASIAir+ to avoid sacrificing a USB slot and to avoid carrying around a power bank. Will the 12V output pump too much power and melt my heater strap, or worse, my OTA? Also, there is a whining sound from the ASIAir when I set the heater control to anything short of full send. Any info on this would be appreciated.