The following is from John Piper’s talk on Martyn Lloyd-Jones, though I had read the works in question long before I had heard the talk.
Martin Lloyd-Jones’ Personal Experiences of Unusual Power
Lloyd-Jones had enough extraordinary experiences of his own to make him know that he had better be open to what the sovereign God might do.
Another illustration comes from his earlier days at Sandfields. A woman who had been a well-known spirit-medium attended his church one evening. She later testified after her conversion:
The moment I entered your chapel and sat down on a seat amongst the people, I was conscious of a supernatural power. I was conscious of the same sort of supernatural power I was accustomed to in our spiritist meetings, but there was one big difference; I had the feeling that the power in your chapel was a clean power.”
Iain H. Murray, David Martyn Lloyd-Jones: The First Forty Years (Piper’s website lists the reference as being in volume 2, The Fight of Faith, p. 221, but that is incorrect. It is in volume 1, page 221.)