What is important here is that your power suplly is rated
5V as anything higher than that could fry your board. The amperage rating
1,2A is a minimum rating so your supply needs to be able to supply anything greater than that.
So your supply
MUST be a 5v rated suply but the amperage could be anything from 2-whatever. (10W-?)
I would prefer a switch mode supply but it does not really matter as long as it is regulated.