H1B Stamped with Employer B but want to work with A employer

Hello ,

My case is i have my renewal petition approved with employer A and transfer petition approved with Employer B.When i came back to India these both Renewal and transfer petitions got approved.

1)I got stamped with employer B(transfer petition) and now i want to work back with employer A, is it fine to work with employer A again,if yes what documents should i show at POE?

2)As usual if i travel using Employer B approval copy at POE then once i reach to US can i again work with employer A having said employer A got approval with i94 and not revoked my H1B or do employer A again required transfer petition?

3)Do i really need a stamping again with my old employer A?

krishna vollala