A hundred envelopes each containing a $100 bill were distributed at the store in Portland, Maine.
People in the shop gasped as they opened the envelopes and one grateful woman, 46-year-old Aurea Parker, even hugged the mystery donor.
The gift of giving: Aurea Parker of Portland hugs the town's 'Secret Santa' after receiving $100
Ms Parker said she was seriously injured in a car accident 11 years ago and had been on disability benefits ever since.
The $100 meant she was now able to mail a Christmas present to her son in Utah.
'I've been sitting around and crying a lot. But this was awesome. I didn't think Santa existed anymore,' she said.
Another recipient, Jim Ward, went to the store to buy a pair of trousers and said he was overwhelmed by the gift, which he planned to use to take his son out for dinner.
'When I opened the envelope I said, "Holy cow". He obviously has a great heart,' Ward said.
Sherry King is all smiles after receiving the last of the 100 envelopes outside the Portland Goodwill store
'I wish I could afford to do the same thing. Giving back is important to me.'
Sherry King of Gorham got the last envelope, and said it would be a 'big help'.
The man behind the gifts revealed he was a local businessman but wanted to remain anonymous - which is why he sent his son to hand out the envelopes as he watched from several hundred feet away.
'It has to be totally anonymous because that is what the spirit of giving is all about,' he told the Portland Press Herald. 'But, yes, I am hoping to start a trend.'
'I'm hoping for a multiplier effect,' he said.
'I'm shocked that every major city in the United States doesn't have at least one secret Santa doing something like this.'
He said he decided to give $10,000 to shoppers at Goodwill because they were the people most likely to be financially stretched over Christmas.
The generous act was inspired by the story of Missouri man Larry Stewart, who handed out $100 bills for years during the festive season and who remained anonymous until shortly before his death in 2007.
