Food campaigner Jack Monroe said she was moved to tears after spotting "remarkable" Smart Price choices on a visit to ASDA.
In the past she has criticised the supermarket chain after items including peanut butter, had been removed from the cheaper line.
Her research showed budget prices across the "big four" supermarket had seen a sharp increase over recent years.
But Jack then found products from the chain's Smart Price and Farm Stores ranges at their local store, saying it had made it the “happiest shopping experience in over a decade”.
After seeing Jack's earlier Tweets, Asda said it would stock its Smart Price and Farm Stores ranges in all 581 food stores and online by March 1 to help its customers with the cost-of-living crisis.
All branches will have the full range of 200 Smart Price and Farm Stores lines, the company said.
It confirmed on Saturday that the full range is already available online.
Jack shared photos of products at Asda in Shoeburyness, Essex, that have reverted to their price from a year ago.
In one tweet, Jack showed a kilogramme bag of rice that was back to its old price of 45p, after jumping last month to £1 for 500g – a price increase of 344%.
The food campaigner was poised to give the store a hard time for excluding an entire group of customers.
But she changed her mind and was left in tears by what she saw on the supermarket shelves which moved her in a way she did not expect.
Jack wrote: “I was very quick to vilify Asda for what I saw as a change of direction for their company, and a watering down of their commitment to an entire group of their customers.”
The company promised to “do better”, she said, as she praised the “remarkable” speed of the turnaround.
“The impact that this will have on millions of people, is impossible to overstate,” Jack said, adding that she “cried, quietly, to myself, in Asda” at the development.
She also wrote: “So I guess I just wanted to say thanks to everyone at Asda who has worked really hard over the last few weeks to bring the missing SmartPrice products back.”
Meg Farren, Asda’s chief customer officer, said: “We want to help our customers’ budgets stretch further and have taken on board the comments about the availability of our Smart Price range made by Jack Monroe.
“We are taking steps to put our full Smart Price and Farm Stores ranges in store and online to make these products as accessible as possible.”
