Travel with new H1B petition and old H1B unexpired visa stamp


I have H1 stamped till next year end. Company A sponsored this H1 for me and i worked for them in US 

for 1 year and back to my home country.


Now i have company B who is filing H1B petition for me, Can i use the H1 stamp of company A with new

approved H1B petition from company B to travel back to US and work in US for company B.


Or is it mandatory to go to consulate for stamping for H1B visa from company B.


Is I-94 given when i come back based on visa sponsor or is I-94 given for employer for whom i will work for.