DC Power Plug and Jack
https://www.denshi-trade.co.jp/documents/dcplug/DCjack.htm
https://faq.as-1.co.jp/faq/show/168555
https://eleshop.jp/shop/pages/acadp_select.aspx
https://www.kamidenshi.co.jp/products/1767
NEC Aterm routers uses EIAJ-04 DC power plug
Most standard power adapter plug uses 5.5 x 2.1 mm