AC WORKS 1 ft. SOOW 10/3 3-Prong L6-30 Male Plug to 6-15/20R 15/20A 250-Volt Connector L630620-012 - The Home Depot
Source 20A 250V 6 pin power connector male and female waterproof connector on m.alibaba.com
Tripp Lite 6in Power Cord Adapter Cable L5-20P to 5-20R Heavy Duty 20A 12AWG 6" - power connector adapter - NEMA L5-20 - P046-06N - Power Cables - CDW.com
Tripp Lite 6in Power Cord Adapter Cable L5-20P to 5-15/20R with Locking Connectors Heavy Duty 20A 12AWG 6" - power - P046-06N-T - Power Cables - CDW.com