Powell was called as a witness in Simpson's doping hearing before the Jamaican Anti-Doping Commission disciplinary panel that will begin a hearing into Powell starting next week.
Both Simpson and Powell tested positive for the same banned stimulant, oxilofrine (methylsynephrine), at last June's Jamaican national championships.
Powell, who blamed his positive test on nutritional supplements, said he only became aware that he and Simpson were both taking similar supplements when both failed drug tests.
"I didn't know she was taking it until after the positive test," Powell continued, backing up what Simpson had told the panel earlier.
More From This Section
Powell told the panel how he was introduced to the supplements by Canadian Xuereb, saying he awoke at 4:45 in the morning and departed for training that started at 5 without having anything to eat.
This, he said, caught the attention of Xuereb, who was staying at his house at the time.
"After a few days he observed (I wasn't eating in the mornings) and told me that I should be taking better care of myself. It was then that he recommended the supplements," added Powell, who spent 10 minutes on the stand.
"There was nothing that rang any alarm bells. No alarm bell. No red flag," said Simpson.