Electrical adapters include ungrounded adapters and grounded adapters. Adapters plug appliance designed for predetermined types of outlets into predetermined types of outlets. Travel adapters are different and allow appliances designed for predetermined types of outlets into certain other types of predetermined types of outlets. Despite different types of plugs in use, travel adapters often manage this kind of usage by bypassing ground or earth wire.
Every appliance does not need to be grounded or earthed, for instance running portable computers and recharging batteries for short periods of time. Convenience and safety are the deciding factors. Appliances that require grounding or earthing for long-term connections need adapters that allow the usage of ground or earth wiring.
Adapters do not allow the change of electrical voltage. Appliances can only handle different voltages either automatically or through voltage switches. Other wise, voltage converters are needed.