David Foster and Katharine McPhee, the Sonny & Cher of power ballads, head to Minneapolis

When piano man David Foster stands in the wings of a concert hall getting ready to perform, his 3-year-old son Rennie “always tries to push me 30 seconds before I’m supposed to go out there and he’s like, ‘Go now, Daddy.’ ”

“He does it to me, too,” interjected singer Katharine McPhee, Foster’s wife. “He’ll say: ‘Go Mommy go.’ And it’s really cute. Of course, he’s cueing us much earlier than we’re supposed to go on. He gets very excited.”

What does Rennie do during the show?

“He conducts,” Foster deadpanned. “He’s with the nanny. Sometimes he sits on the side of the stage and watches us.”

Expect some back-and-forth, good-natured bickering when Foster, the producer/songwriter behind so many over-the-top pop ballads, and McPhee, “America Idol” runner-up and star of TV’s “Smash,” team up Wednesday in Minneapolis at the State Theatre.

“The basic ideas [of their show] are scripted but we’ll usually wander,” Foster explained in a joint telephone call from Los Angeles. “And we find new things like her throwing a dig at me. It’s really loose.”

“We talk about how we ended up onstage together,” McPhee picked up. “All the years we were doing gigs as friends and colleagues and then we ended up married, acknowledging how unconventional it is. We tell our story. We think we’re pretty funny.”

So what married musical couple do they most resemble — Sonny & Cher, Steve Lawrence & Eydie Gorme, Captain and Tennille, Susan Tedeschi and Derek Trucks?

“The only one I know is Sonny & Cher,” said McPhee, 40.

“You never heard of the Captain and Tennille?” asked Foster, 74.

“I don’t know any of their songs,” McPhee continued.

“Sonny and Cher with the banter, at least,” Foster said. “And maybe musically Daryl and Tennille.”

Then he starts singing the chorus of “Love Will Keep Us Together,” Daryl Dragon and Toni Tennille’s 1975 smash.

“Who wrote that? Neil Sedaka,” Foster said.

Foster is someone who pays attention to credits. Because he has a plethora of them. He has earned 16 Grammys, a spot in the Songwriters Hall of Fame and other accolades for his work with Céline Dion, Barbra Streisand, Whitney Houston, Michael Bublé, Josh Groban, Andrea Bocelli and many others. His compositions include Chicago’s “Hard To Say I’m Sorry,” “Whitney Houston’s “I Have Nothing,” Earth Wind & Fire’s “After the Love Is Gone” and the Bocelli/Dion classic “The Prayer.”

McPhee’s credits include the TV shows “Smash” and “Scorpion,” the films “You May Not Kiss the Bride” and “The Tiger Rising,” Broadway’s “Waitress” and, of course, “American Idol” in 2006. Her “Idol” season featured a cast full of careerists, including champ Taylor Hicks, rocker Chris Daughtry, Nashville personality Kellie Pickler, the late gospel singer Mandisa, pop singer Elliott Yamin and the Twin Cities’ own Paris Bennett.

“‘Idol’ was a boot camp,” said McPhee, whose mother and sister later served as vocal coaches on the talent program. “Then coming off the show, I suddenly perform concerts and I had no idea how to do that. I spent all my early 20s learning how to do it. A lot of times it was humbling because it was for 100 people in a place that could hold thousands at county and state fairs. For me, it was a great launching pad.”

Foster, who has been a coach on “Idol,” said the contestants are “good singers but not good performers. That’s why none of these shows have made a star in the last decade. They’re entertaining to watch.”

Foster and McPhee met on “Idol” but didn’t get together until 2017, marrying two years later.

McPhee describes Foster as “irreverent, spontaneous, funny, charming and he has great comedic timing.”

Foster describes his wife as “beautiful, irreverent, clever, silly, adventurous.”

He thinks people would be surprised to know that she’s a homebody. “She doesn’t like to go out, which is constantly a tug for us ‘cause I like to go out.”

McPhee countered: “He is a bit of a nervous nelly. He’s a helicopter dad. He’s not adventurous at all.”

Another thing: Both are left-handed.

“Does that mean anything at all when you’re married?” Foster asked rhetorically.

Sounds like it could become a bit in their show.

They do a bit about appearing together on “The Masked Singer” in 2021 as Banana Split.

“It’s not easy to sing in those things,” McPhee pointed out. “It makes it very difficult to have a good vocal. We enjoyed it. We were very competitive.”

Foster and McPhee recorded a 2023 Christmas album together. She is slowly working on another solo album, with Foster’s help.

He hasn’t been in a recording studio as a producer for other artists for eight years. He’s been working on the long-gestating musical “Boop,” based on the cartoon character Betty Boop.

“We had a great six-week run in Chicago in December and we worked out a lot of the things we wanted to fix and didn’t know we needed to fix,” he said. “This last week, they were in rehearsal again in New York. We plan on being on Broadway in late winter or early spring of ‘25.”

Meanwhile, Foster is busy being Dad to Rennie, his first son and McPhee’s first child. He has five daughters from his previous four marriages.

“He’s decided he doesn’t want to play the drums anymore,” Dad pointed out of the youngster.

“It’s nice to have silence around the house,” McPhee added.

When: 7:30 p.m. Wed.

Where: State Theatre, 805 Hennepin Av. S., Mpls.

Tickets: $60-$100, ticketmaster.com