What does this symbol mean on my Samsung travel adapter?
That's the Ukrsepro mark. It means the product has passed the certification of UkrSEPRO, the safety certification requirement symbol for trading in the Ukraine region.


  Scope of products covered by the above regulations include but not
  limited to the following:
  
  
  Information technology equipment
  Audio and video equipment
  Household and similar use appliances
  Lighting products
  Electric tools
  Low-voltage electrical equipment
  Electrical wires and cables
  Switches for circuits, installation protective and connection devices
  Telecommunication terminal equipment
  Manufacturing equipment for food, meat, dairy industry, trade enterprises, catering and food processing enterprises
  Electrical machinery
  


The norms and standards products have to comply by are set by the Ukrainian Research and Training Center of Standardization, Certification and Quality Issues (UkrNDNC, a state enterprise), the Ukraine representative for ISO, IEC, CEN, CENELEC, ETSI etc. Also known as DSTU.

Importers and manufacturers are allowed to prove conformity by submitting self-declaration (like CE in Europe). However, this declaration must additionally be registered with the accredited authority (regulated by the National Accreditation Agency of Ukraine, NAAU). See also the EC Trade Market Access Database, paragraph "Standardisation" on Ukraine.

Likely (thanks to dlatikay for pointing out the obvious), the symbol represents a tryzub, a trident prominent on the Ukrainian Coat of Arms and which has been important throughout Ukrainian history.