For Saint Kitts and Nevis the records list Types A, B and G at 230 V and 60 Hz. No surprises on voltage: Saint Kitts and Nevis runs at 230 V, the same range as at home in the UK. 60 Hz rather than 50 Hz matters only for motors and timers, not for power supplies.
The same socket system is used in Saint Vincent and the Grenadines, so one adapter covers all of them. Travelling further to Guadeloupe and Greenland means a different adapter. 2 of the 31 destinations in North and Central America share the plug types of Saint Kitts and Nevis.
Protective earth
Grounded and ungrounded sockets may occur
Earthed sockets (Types B and G) and unearthed ones (Type A) exist side by side. For metal-bodied appliances the protective-earth path is what matters.