Does a palate expander decrease snoring?

Depends: Palatal expanders can be a tool in the management of airway obstruction. By expanding the palate they improve the nasal airway(just above the palate). They are often more useful very early teens. Some have even used them in adults. They can decrease snoring if the reason for the snoring is due to nasal airway. Snoring is due to multiple issues and the soft palate is usually one.

Palatal Expander: Generally, palatal expanders make room for upper teeth -- that's it. If palatal expansion occurs in children younger than age 6 -7, it may actually help expand the floor of the nose as the palate expands. For adults, palatal expansion will do little for snoring. Snoring means there is airway obstruction, but where? Consider seeing an ENT for a complete exam of your airway to determine why.

Maybe: There is not a definitive link in the literature yet, but many parents have reported this to me as well for kids undergoing expansion. Snoring is adolescents often is induced by a constricted upper airway via swelling of the adenoids and/or reduced nasal space. Palatal expansion indirectly affects the airway and could improve the issue in kids but unlikely in adults. An ENT eval is advised.

Depends: If your upper jaw is too narrow a palatal expander for an adult will not correct palatal width, only top teeth outward. A palatal expander coupled with upper jaw surgery will permit widening of the upper jaw (surgery not need in kids). This may help reduce snoring. Please note that after expansion braces will be needed to properly position teeth.