  We derive the Hawking radiation power equations for black holes in
asymptotically flat, asymptotically Anti-de Sitter (AdS) and asymptotically de
Sitter (dS) black holes, This is done by using the greybody factor for these
black holes. We observe that the radiation power equation for asymptotically
flat black holes, corresponding to greybody factor at low frequency, depends on
both the Hawking temperature and the horizon radius. However, for the greybody
factors at asymptotic frequency, it only depends on the Hawking temperature. We
also obtain the power equation for asymptotically AdS black holes both below
and above the critical frequency. The radiation power equation for at
asymptotic frequency is same for both Schwarzschild AdS and
Reissner-Nordstr\"om AdS solutions and only depends on the Hawking temperature.
We also discuss the power equation for asymptotically dS black holes at low
frequency, for both even or odd dimensions.
