The answer depends on what sort of charging you're looking for -- a 65W power bank won't fully charge the internal battery more than once -- or slightly more depending on which battery you have. If you're looking to charge the battery more than once using the power bank, choose something with a higher capacity.  
Good day,Latitude 5290 2-in-1 Visual Guide page (need to scroll down some) says AC has to have output of 45-65WI wonder if this powerbank I found on Amazon shall be sufficient? Looks so for me, but I would be glad if someone confirmed since I am not very keen on it and also do not want to ask for refunds later etc.Thanks!!!
Powerbank for Latitude 5290 2-in-1