Well here are a few options ;
1) Bombay Bhel Puri
G-7, Near Midland Book Shop, South Extension 1, New Delhi
2) Imly
Shop F-20, Hog Market, Rajendra Place, New Delhi
3) Prince Paan
M 29/5, G.K. Part 1, New Delhi
4) Bengali Market
Babar Rd, Todermal Road Area, Mandi House, New Delhi
5) UPSC Chaat Wala
Main Bhawana Road, Pehladpur Banger, New Delhi
6) Social Offline
.
Personally speaking I have been to 3 of these places social offline, prince paan & UPSC Chaat. Out of the lot my favourite is the one at UPSC its a small shop at the side you UPSC and offers a variety of other food as well along with a spicy tangy bhel just the way it should be & if the bhel gets too spicy for you there is rose lassi to save you.