From the Super Mario Wiki, the Mario encyclopedia

First appearance

Dr. Mario World (2019)

Effect on player

Adds extra capsules prior to starting a stage

Capsule+ (also known as Capsule Boost) is a bonus item in Dr. Mario World. It gives players extra capsules for use in stage mode. All players start out with a free use of Capsule+, where subsequent uses of the item can be bought with 10 diamonds. For timed stages, these items are replaced by Time+ boosters. If a player fails a stage too many times in a row, Toad helps the player with a free use of it.