하고 vs 에다가

[한글사랑]

S: teacher, what's the difference between 피자하고 햄버거 먹고 싶어요 and 피자에다가 햄버거 먹고 싶어요? 

T: 안녕, 우메이마... 좋은 아침.

피자에다가 햄버거 먹고 싶어요

(피자 먹고 싶어오 그거 에다가 햄버거 먹고 싶어요)

I want to eat pizza, on the top of that, I want to eat Hamburger.

피자하고 햄버거 먹고 싶어요.

(피자 먹고 싶어요 그리고 햄버거 먹고 싶어요)

I want to eat pizza and Hamburger

both are almost same. but the nuance of the sentence is little bit difference. for example...
if someone ask

뭐 먹고 싶어요? and then,
this answer is normal

피자하고 햄버거 먹고 싶어요 

but ~ 에다가....do you remember ~에 menas postposition "to"(time or location)?

so ~에다가 means on the top of that(sounds like it has a direction "to" and already have something and add another things/ ~다가 while doing something : 가다가 while I am going => the nuance is "present")
see these example sentence. 

이거 어디에(다가) 놓을까요? where should I put this?

거기에(다가) 놓으세요. put there.

커피에다가 설탕을 좀 넣어 주세요. plz put little sugar in the coffee.

책에다가 낙서를 하지 마세요. don't write on books.

빵에다가 꿀을 발라 드세요. apply hony on bread and eat it.