Would this be similar to what your referring to?

Parkworld 691715 Shore Power Adapter Regular 15A 5-15P Male Plug to Marine 50A SS2-50R Female (Two hots bridged) with Locking Ring https://smile.amazon.com/dp/B01M0W1IOY/ref=cm_sw_r_cp_api_glt_fabc_QYDN0VQXH5RGQP8ST115