Type B vs. Type O

Type B adds a round grounding pin to Type A's two flat blades -- NEMA 5-15, the most common outlet in North America. The ground pin is deliberately longer than the power blades, so it connects before and disconnects after them, a safety-sequencing feature shared with several other grounded plug types worldwide.

Type O is Thailand's standard, introduced in 2006 -- three round pins whose earth-pin offset happens to numerically match Type B's, letting Thailand's real-world hybrid sockets also accept American Type A/B and European Type C plugs. Pure single-standard Type O outlets barely exist in practice.