"Serpent power" is an expression referring to Kundalini (Skt. for coiled one,) a type of energy that is traditionally thought of as lying coiled at the base of the spine. In diagrams of the subtle body, it is depicted as a serpent or snake.
J. F. shares [Kagyu email list, Jan. 2001] the experience of a kundalini awakening while training with a Hindu guru in the early 1980's:
1. Definite opening/awakening occurred . . . how "asleep" we all are . . . that level of
experience was like literally waking up from a dream.
All of the above are just words, though. Every time I have tried to put into words the understandings that arose, words fail me, but the understanding is there and fuels my fire!
Key word is "awaken". . . nothing was really added, blocks were removed and the inherent wisdom was exposed for a time. This happened to quite a few people around him, but the episode would end, the obscurations would take over . . . I could literally see them "cloud over" the radiance towards the end . . . and the homework would begin, daily practices, lots of "mind training" and a "gradual path" start, something few had the patience or dedication for.
So . . . it was a wonderful experience, truly pivotal in my life, but would have come to naught without the homework . . . one of the aspect of Tibetan Buddhism that attracted me was the willingness of the students to get down into the nitty-gritty hard work. That and the incredible inner science passed guru to disciple for hundreds of years.
Since then I have read about a lot of similar incidences in many traditions, mostly eastern . . . the Tibetans obviously have access to such siddhis, I've read numerous descriptions of such. [For example, in] The Life of Milarepa by Rechungpa, after such an episode near the end of his life Milarepa admonishes his followers:
[Milarepa] seemed from the stories to certainly have the ability to "light up" his disciples on occasion . . . give them a "taste," so to speak.
Unfortunately the Hindu adepts at this seem to be content to engender a sort of addiction to the experience, in that tradition there was certainly a tendency to "go for the bliss." Still, for me it is nice to know without a doubt that we are, indeed "pure light masquerading as flesh and bone."
Lama Yeshe, who was among the first to introduce Westerners to Tibetan Buddhism, did not shy away from the use of the term kundalini in The Bliss of Inner Fire (Wisdom Publications, 1998.) NB. The book is about the commentary by Je Tsongkapa on the Six Yogas of Naropa.