We have an LG 27" LED TV with built in DVD
on our boat. it included a power brick that produces 12VDC which feeds directly into the TV which was the main reason we purchased this model. First thing I did was wire it directly into the boats DC supply, throwing away the brick. The telly works directly off all voltages (up to around 14.2 or so) without complaint. We do use it for TV reception
around our local cruising grounds and rarely use it to play a DVD. What we also use a lot is a USB hard disk loaded with hundreds of videos and photos. This hard disk is powered by the TV USB port and that little LG can play more video formats than either of the two big screens we have at home. In fact, if I were to replace the TV in the future, I wouldn't even bother with the DVD option (although I'd consider a Blu-Ray) as the USB hard disk takes up nothing spacewise compared to a stack of hundreds of DV disks.
Also, I can't remember the exact numbers, but the particular screen
size we purchased had a specified power consumption
of 36 watts typical which is a lot less than the value for 32" screen
sized and bigger sets and struck me as a reasonable size to power usage compromise for our particular use.