Type D vs. Type O

Type D is the old British 5A standard (BS 546, 1934) -- three large round pins in a triangle. It predates and is completely incompatible with the UK's later Type G, and remains the primary domestic standard in India, Nepal, and Sri Lanka today.

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.