Your expansion dock is a goner.
(Assuming you are talking about this dock https://onion.io/store/expansion-dock/ )
The square IC in that board is a USB-serial chip (most likely CP2102.)
Usually when it was hit by high voltage even in a brief moment, it will be damaged and causing shortage.
BTW, the power switcher IC (5 --> 3.3V IC, the 5-pin one) may have also died.
This IC is very useful since it has the special "zero droipout" design.
On the other hand, it will also meet its instant death when power supply goes above 5.5V, even briefly.