My belief is that vampires are the descendents of the Nephylim, they are all children of man and angels, not necessarily physically just Lilith's but she called and they came to her and since then, I believe, they have identified her as their mother in the way Christians consider 'God' to be their father but it a far less twisted way.
I don't beleive that everyone who needs to 'feed' is a vampire. I think that those of us whose energy level is higher than a normal human's can't be sustained by human bodies, they just can take in enough energy, so we have to take in more from the lifestream/pranic force which we get from blood/energy. I don't think there is any such thing as a psychic or a sanguinarian vampire as a type... we all need to take in prana. The only difference between them is the matter of choice and inclination as to which source is used.