Anything that requires AV power (aka a wall outlet) for power is going to have the strongest, most mind blowing vibrational power. Rechargeables are second to corded toys and still pretty powerful. I suggest you go to the vibrator page, click "Refine By" at the top of the menu on the left, and scroll down to select "Powered By".
These will generally be your strongest possible toys, though there are a few that take batteries that are powerful too. But at the top of the list are external "wand" massagers like the Hitachi or Fairy.
If you want to include ones that take batteries and specifically look for the strongest of them, just refine more by looking for toys with "Vrooms" of at least 4 or 5.