EIAJ RC-5321
This is a unique-looking barrel connector, apparently intended for providing a DC output jack (most DC jacks are used for power input).
Possibly available in multiple voltage ranges, the one for voltage classification 2 (3.15 to 6.3 V) has an outside diameter of 4.75 mm and a protruding pin of 2.5 mm diameter.
Previously known as EIAJ RCX-5321.
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