Check the current rating of the manufacturer's AC supply. You will want something that can match that or better. A DSLR can easily pull several amps for short periods during focus and image processing phases. I use a 3rd party AC supply for mine and it is rated for 8v @ 3A. I tried running it from a 1.5A supply once. It would power up, but would shut-down as soon as I tried to take a photo.
Most DSLRs these days use LiPo packs. A 2-cell LiPo battery or a 6-cell NiMH pack will put out the right voltage and should not require a regulator.
(Of course the manufacturer will say that any electrons that do not originate from an authentic manufacturer supplied power source will invalidate your warranty and may damage your camera).