When positional encodings/embeddings are used, the word 'good' in these two sentences:

‘The food was good, not bad at all.’

and 

‘The food was bad, not good at all.’

will have different embeddings in the Transformer's output.

When positional encodings/embeddings are used, the word 'bad' in these two sentences:

‘The food was good, not bad at all.’

and 

‘The food was bad, not good at all.’

will have identical embeddings in the Transformer's output.

Positional encodings/embeddings encode the words themselves, and do not encode their positions.