In a testimony to a congressional committee on Wednesday, Powell pledged to "act as appropriate" to defend an economic expansion threatened by trade disputes and a global slowdown.
The comments fuelled talk that the Fed could cut rates by more than expected at its July meeting, pushing bond yields in the euro zone back down after a sharp jump following stronger-than-expected French and Italian economic data on Wednesday and new bond supply.
"We saw some big moves yesterday and then the Fed came out and said it stands ready to ease policy even after the strong jobs data last Friday," said Pooja Kumra, European rates strategist at TD Securities in London.
"When ever we get (price) dips in this market, it is taken as an opportunity to buy."
Having posted its biggest one-day jump since April on Wednesday, Germany's 10-year government bond yield dipped to minus 0.32%. It is about 9 bps above record lows hit last week.
Most other 10-year euro zone bond yields were 1-2 bps lower in early trade, with focus turning to the release of the European Central Bank's June minutes later this session.
Analysts said focus was on whether the ECB's Governing Council has started discussions about a return to asset purchases to lift growth and inflation.
German annual inflation accelerated to 1.5% in June, remaining below the ECB's target, data on Thursday showed.
"The ECB accounts cover a meeting which differed greatly from the rhetoric that has emerged since," analysts at Mizuho said in a note.
"This allows the market to disregard any hawkishness, but the accounts will still be looked to for hints on the nuances of the bank's reaction function."
Money markets fully price in a 10 bps cut in the ECB's deposit rate in September, while many economists believe a return to asset purchases is increasingly likely given below-target inflation and uncertainty sparked by a global trade war.
The European Commission lowered its estimates on Wednesday for euro zone growth and inflation, saying uncertainty over U.S. trade policy posed a major risk to the bloc.