ADP private payrolls are expected to show that 200,000 positions were added in March, just under the 205,000 projected for the government's nonfarm payrolls Friday.
But Yellen could continue to impact markets, as Fed watchers weigh her words against expectations. Citigroup late Tuesday cut back its forecast for rate hikes to just one increase in 2016, calling her an "uber dove" following an afternoon speech in New York.
Stocks climbed, and the Dow and S&P 500 both closed at 2016 highs, in a post-Yellen rally. The rose 0.9 percent to 2,055, and the Dow was up 0.6 percent at 17,633. Treasury yields slid to their lowest level in two weeks, and the dollar sagged.
Chicago Fed President Charles Evans will appear on CNBC's "Squawk Box" at 8:30 a.m. EDT. Evans also appears at 1 p.m. at the Forecasters Club of New York. He is viewed as one of the more dovish members of the central bank.
Yellen's speech Tuesday came just days after several Fed officials said it should start hiking rates. Yellen, on the other hand, emphasized the slow pace of expected rate increases and pointed to the risks to the Fed's forecast and inflation expectations.
"They are sending a very confused message. I think she was letting you know that she's a lot more dovish than the bulk of the board," said Ward McCarthy, Jefferies' chief financial economist.
"Every once in a while, there's a disconnect between the way Fed communicates policies with the rest of the world, and we're in one of those periods right now," he said.
McCarthy said he is watching Wednesday's ADP data to see if small and midsized businesses continue to hire, an important sign of a healthy labor market.
Credit Suisse economist Dana Saporta said in the past three March ADP reports, the ADP private jobs were higher than the government payrolls by an average 41,000 jobs. In 7 of the last 8 years, she said the government's nonfarm payrolls came in below consensus.
Saporta expects the government to report 190,000 nonfarm payrolls when the March employment report is released Friday. Of those, 185,000 are expected to be in the private sector.
There is also Energy Information Administration oil inventory data at 10:30 a.m. EDT and weekly mortgage applications at 7 a.m.
Correction: Saporta said in the past three March ADP reports, the ADP private jobs were higher than the government payrolls. An earlier version misstated that fact.