Early 1e sources and the more recent editions of D&D make exactly that distinction between devils and demons. Devils (2e: Baatezu) are lawful evil, while demons (2e: Tanar'ri) are chaotic evil, forever fighting the Blood War about something they're gonna figure out after the carnage. Although they aren't standard fare in AD&D, a lawful evil, or lawful neutral pendant to the classic paladin would also have to stick to their code of honour or lose their powers. While their chaotic good colleagues in the Old Empires would lose their powers if they held law above good.
