There are some things to think about when feeding DC. Don't forget a fuse, a common mode filter and some filter caps. The filter caps are partially to give a low impedance source at the switch and also to prevent EMI. Another consideration is the 220VAC will rectify to give about 300V DC. In other words 220V DC isn't enough and that can cause major problem if the switcher has not been designed to operate at that voltage.
Another consideration is that some SMPS's (mainly lower voltage input ~120VAC types AFAIK) use a voltage doubler and that requires an AC input.