China's own port fees against whom? Reciprocal port fees against US made ship is useless because US shipbuilding industry is practically non-existence (I'm not against putting one up anyway just to bury the very idea of US shipbuilding industry though).
What the US port fees does is essentially increase the competitiveness of SK and Japan shipbuilding industries against China. But not by much, I predict major shipping companies will magically shit out a bunch of subsidiaries to exclusively handle shipping route to US where they concentrate all their non Chinese made ship.
Again the american overestimated their importance in global market, US bound shipping route is just a small fraction of global shipping volume much less than China's shipping volume in fact. If they keep this up it will just further shrink their volume and destroy their port business. At this point it will be cheaper to just unload cargo in Canada and Mexico and move those cargo through land route into US.