Powell reaffirmed the central bank's intent to encourage a "broad and inclusive" recovery of the job market, and not to raise interest rates too quickly based only on the fear of coming inflation.
"There's been some buying on the back of a lower dollar and the possibility of a strike at Escondida (copper mine in Chile)," a copper trader said. "But the rally does seem to have to run out of steam."
An overhaul of Chile's market-orientated constitution is underway and the country is debating whether to increase royalties on miners.
Meanwhile, Yangshan copper premium climbed $1.50 to $38.50 a tonne on Monday, rising for the first time since February and signalling early signs of improved demand for imported metal into China.
The most-traded June copper contract on the Shanghai Futures Exchange dipped 0.5% to 76,380 yuan ($11,887.94) a tonne, clawing back from early losses of 2.5%.
The first half of April was still weak, but smelting activity increased throughout the rest of the month, satellite service SAVANT and broker Marex said in a joint statement on Wednesday.
"The platform now suggests we are seeing the effect of that price rally with a strong increase in smelter activity in the latter part of April."
The exchange, the world's oldest and largest market for industrial metals, announced a proposal in January to move to full electronic trading and held a consultation.
"The LME received an unprecedented volume of feedback ... with 192 individual responses," it said.