The reaction on Tuesday - evidence of the relationships Powell has built during his years at the Fed and of the importance of the central bank to global financial markets - follows pushback from several lawmakers in President Donald Trump's Republican Party on Monday, including members of the Senate Banking Committee who have the power to block the president's nomination of a more biddable successor to Powell.
The current Fed chief's term ends in May. Powell revealed late on Sunday the US central bank had received subpoenas from the US Justice Department about what he told Congress regarding the $US2.5 billion ($A3.7 billion) renovation of the Fed's headquarters in Washington.
Powell said the probe was a pretext meant to pressure the central bank to slash interest rates, as Trump has long wanted.
"We stand in full solidarity with the Federal Reserve System and its Chair Jerome H. Powell," the heads of 11 of the world's largest central banks said in a rare joint statement.
"Everyone we know believes in Fed independence," JPMorgan CEO Jamie Dimon told reporters on a conference call on Tuesday.
"This (probe) is probably not a great idea, and in my view it will have the reverse consequences of raising inflation expectations and probably increase rates over time."
Independence from government influence has been the key foundation of modern central banking. It remained the unquestioned standard until Trump started demanding lower rates and putting pressure on individual policymakers when they failed to oblige.
Trump on Tuesday again demanded Powell lower interest rates "meaningfully" after a government report showed consumer prices rose 2.7 per cent in December from a year earlier.
The president was slated to visit a Ford truck factory in Detroit to put a spotlight on US manufacturing and his efforts to tackle high consumer costs.
Meanwhile traders kept bets that still-too-high inflation would keep the Fed on hold regarding rates until June.
The heads of the Reserve Bank of Australia, the European Central Bank, the Bank of England, the Bank of Canada and seven other institutions said Powell had acted with integrity and that central bank independence was crucial for keeping prices and financial markets stable.
"The independence of central banks is a cornerstone of price, financial and economic stability in the interest of the citizens that we serve," the statement said.
Other signatories included the central bank chiefs of Sweden, Denmark, Switzerland, South Korea, Brazil and France, as well as top officials at the Bank for International Settlements.
