You can order the Cisco 1941 with an AC or PoE type of power supply. The Cisco 1941 does not offer a DC version of the power supply, and it does not support an external RPS.
The Cisco 1921 ships...
You can order Cisco 2911, 2921, and 2951 with a power supply that is AC, PoE, or DC. During product configuration you must select the type of power supply and the power-supply cable you need for use...