ETHELBERT (m): Derived from a compound of Anglo-Saxon æthel- "royal," "noble" + beohrt/berht "bright," this last derived from an Indo-European root *bherəg- "to shine," "bright," "white" (Calvert Watkins, The American Heritage Dictionary of Indo-European Roots, 2nd ed., 2000, p. 11). Æthelberht I of Wessex (ruled 860-865, a brief reign bedeviled by Viking raids) was the third son of Æthelwulf of Wessex. Æthelbert was preceded by an older brother Æthelbald (co-king with his father ca. 855-858, then full king 858-860), and was succeeded by his younger brothers Æthelred I (ruled 866-871), and, finally, Alfred [Ælfred] the Great (ruled 871-899). Alfred's grandson Æthelstan (ruled 924-939), the victor of Brunanburh, is the first king of all England (rather than Wessex).
The history of the Anglo-Saxon period was not much studied until the late eighteenth and early nineteenth centuries, but New England does have the example of Ethelbert Child Lyon (1744-1787) of Woodstock, Conn., and Holland, Mass., a son of Moses and Grace (Child) Lyon of Woodstock. Moses Lyon, a Yale graduate, apparently enjoyed choosing learned names for his numerous offspring. The 1850 census shows 216 men with the name Ethelbert.
The name ALBERT developed from ADELBERT, a cognate Germanic form of both elements of this name. (Speak "Adelbert" fast, say five times, and you'll see how that first consonant falls out; ALICE evolved in much the same way from forms such as ADELICIA.)