As an infant adoptee born in the early 1960s in a state with very tight laws concerning closed records, DNA was instrumental in confirming the identity of both sides of my birth lineage.
And has revealed that the men on my birth father's side have been, shall we say, generous with their DNA samples for generations. Lots of high confidence 2nd cousins (a great grandparent in common) whom the regular family didn't know we're related.
DNA testing can and does deliver surprises, not all of them positive. My mother-in-law discovered she has an ancestor from West Africa. I guarantee you 100 percent that story was never told by her pasty pale family who brag about their German heritage.