@Cub C
Too much Voltage to the charging port will certainly damage devices however that's unlikely/impossible to happen using a standard direct USB connection to a PC. Additionally, a Garmin device like most well-designed portable devices, has internal circuitry that protects against too high a current when charging. It seems possible the devices have indeed been 'soft-bricked' due to the hub you used - when connected directly to PC using a standard USB data cable, Garmin Automotive devices will default to trying to connect either in MSM/MTP or in "Garmin Mode" (aka preboot mode) as well as safely taking charge for the internal battery if required. Provided the power source is supplying Voltage in the correct range (computer USB Sockets as you'd know, are ~5V DC), then the device will only draw the Current it needs (e.g. A USB3 socket does supply a far higher current than needed but the device won't take anywhere near that amperage). Due to both your devices having problems following use of the hub it's likely that was the common cause. Possibly its use, which as previously stated isn't recommended, has caused some temporary problem preventing a normal boot process i.e. a soft-bricking. If they are 'hard-bricked' due to physical damage to the internal circuitry then it's not possible to recover them using any software methods.

Working on the basis that the problem is indeed a correctable soft-bricking, you should do the following in order with each device:

  1. Confirm that they can both enter preboot mode. Read here: [Only registered and activated users can see links. ]
  2. Confirm that you are about to use the correct firmware by checking the device's HWID. Read here: [Only registered and activated users can see links. ]. Then first try re-loading the original (not cured) firmware in preboot mode after making appropriate RGN files from GCDs using Cure3 application: [Only registered and activated users can see links. ]
  3. If reloading original in preboot doesn't change anything (that method directly flashes the required firmware regions) then use Cure3 to make cure fw and load it to allow removal of corrupt files, or to re-format if absolutely necessary. (Re-format only using [Only registered and activated users can see links. ]). Read carefully here too: [Only registered and activated users can see links. ].

If you need further help, post again saying exactly what you've tried and if anything changed. See here too: [Only registered and activated users can see links. ]