I was having issue with abysmal overhangs, even despite using supports, so decided to find a solution (I'm printing in PETG currently).   
I found out I'm not the only one, and people often swap the stock 0.11A fan to for a 0.22A fan, and that they print better ducting. I don't have proper ventilation for ASA at the moment, so I decided to just swap the fan and see what will happen. So I did that and it turns out... the quality dropped.   
  
I printed overhang test before and after. I was surprised even before the swap, because the test came out much better than expected (and much better than real prints). But I was even more surprised after it turned out, that the swap made the things even worse. Previously the text markings which side the overhangs points was legible, now they are not. There is bunch of stringing. And while overhangs at 70 got slightly better in some aspects, got worse in others. And the 80 one got much worse.   
  
I tried lowering the fan speed in Orca slicer from 30% to 15%, and for overhangs from 90% to 70%, but it didn't improve anything, it actually got even worse...   
  
I'm still planning to print the better duct once I will be able to print ASA. But I'm wondering what happened and why quality got so much worse. Did the filament got wet in the span of couple of couple of hours? Did I messed up the print head during the swap? Or the new fan is bad? Any ideas?

Qidi Q2 - I swapped part cooling fan for a more powerful one and print quality dropped