Hall & Oates struggled to ride soul train while Train was on the right track at Xcel Energy Center

Damn the hipsters.

Those cooler-than-thou cognoscenti — and critics, too, for that matter — embrace hip musical acts and then abandon them if and when the stars gain mainstream success.

Case in point No. 1 — Hall & Oates. They were groovy blue-eyed soul men in the early '70s on KQRS in its pre-classic rock days before Daryl Hall & John Oates became 1980s synth-pop MTV mainstays.

Case in point No. 2 — Train. They were alluring alt-popsters in the '90s on then-cool Cities 97 before becoming Top 40 fodder in the '10s.

Even though they are a generation apart in age, these similarly fated bands have teamed up for a co-headlining tour that landed Wednesday at Xcel Energy Center.

Hall & Oates, the bestselling duo that was inducted into the Rock & Roll Hall of Fame in 2014, proved once again to be a guilty pleasure. Except they were more pleasurable last year at the X when collaborated with Tears for Fears, another oldies act.

The difference this time was Hall was guilty of no longer being in top vocal form. Although he was impassioned and enthusiastic, his voice sounded worse for wear. Singing deeper than ever, he was sometimes hoarse and just didn't display the vocal range of the past.

If it wasn't noticeable on all the Hall & Oates numbers when six backup singers (including Oates) helped him out, it was apparent when Train's Pat Monahan joined Hall & Oates for three selections during their closing set. Monahan, 49, unleashed his pure high tenor while Hall, 71, once a high-voiced soul singer, offered raspy weariness on "Philly Forget Me Not," their new joint single that they co-wrote as "a paean to Pennsylvania" because they were both born there.

Then Monahan, hardly Hall of Fame material, sparkled on H&O's 1979 nugget "Wait for Me" and Train's tune, "Calling All Angels," while Hall struggled with his soulfulness.

Thereafter, however, Hall seemed to gain some vocal momentum, especially on the encore of "Rich Girl" and "You Make My Dreams," both buoyed by splendid backup vocals and a top-notch band.

Throughout their 95-minute set, H&O gave their sidemen, especially guitarist Shane Theriot and saxophonist Charles DeChant plenty of solo opportunities. In fact, the instrumental excursions extended the disco-y hit "I Can't Go for That (No Can Do)" to a full 13 minutes on Wednesday.

And let's not forget about Oates, the short dark-haired half of the duo, the one with the mustache, now salt-and-pepper with a goatee. He held his own vocally on the duet cover of "You've Lost That Lovin' Feeling" during which Hall couldn't seem to find his upper register. And Oates shined on vocals and guitar on the moody, spacey "Is It a Star" from the duo's 1974 experimental album.

During Train's 65-minute set, it was obvious that Monahan was eager to please the crowd of 10,000. He grabbed fans' phones to snap selfies, tossed souvenir T-shirts into the audience and praised the crowd for being "so much better than Green Bay."

Except on 1999's breakthrough alt-pop favorite "Meet Virginia," Monahan wore his inspirations on his sleeve — from the Elton John on acid of "Drops of Jupiter" to the sing-songy "Heart and Soul" to the simplicity of "Play That Song" to the breezy catchiness of Jason Mraz on the recent hit "Hey, Soul Sister." Always aiming to please, Monahan and Train even covered Led Zeppelin's "Heartbreaker" to prove that he knows how to walk the line between cool and commercial.

Twitter: @JonBream • 612-673-1719