Smith (26) has switched from Stamford AFC after the Daniels agreed to waive United’s seven-day approach for the experienced frontman.
The Grantham-based powerhouse has previously played for the likes of Spalding United, King’s Lynn Town and Grantham Town.
Boston-born Adams (18), meanwhile, has re-joined the Pilgrims after a four-year stint with Nottingham Forest. He had originally played in United’s youth system before switching to the City Ground.
Updated 16:43 - 1 Aug 2016 by Craig Singleton