That takes 9V AC, so not so easy to power in the field. Best bet is to get a 12v battery (which is DC) and use it to provide power to a power inverter. The cheaper power inverters create a stepped interpretation of an AC sine wave, which might add some nasty noise to the recording, though this probably depends on the design of the DMP3.
Better bet would be to get a true sine wave inverter for your power inverter. Coupled with a 12v battery, that would actually give you better AC power quality than a wall outlet. But true sine wave inverters are pretty expensive.