Bob Brown has covered most of the salient points in his answer but I did want to point out that there is one significant disadvantage:  Complexity.   You are increasing the complexity of your application to some degree, lesser (in the case of adding a pepper to the hash where you need to think about key management as well as storage of password hashes and salts) or greater (in the case of implementing something more sophisticated like AES and needing to store IVs or Nonces and possibly tags/MACs as well as the output, the salt, and managing the key(s).) 

So, is the value you're going to add sufficient to justify the additional cost of complexity?  You'll have to answer that question for your application.  I'd would say that it generally doesn't, while there certainly are cases out there where it does.   

In any case, as Bob mentioned, you need to start with a strong foundation and move to a better hashing algorithm like Bcrypt regardless of whether you decide to encrypt or not.   

Are there any disadvantages to encrypting the password hash?
Is potential energy and "work done" the same thing?

If they are not one and the same thing then why is potential energy always associated with "work done"?

Could you explain me with some examples?
