A major concert for a minor but fanatical portion of indie music fans, Neutral Milk Hotel’s sold-out all-ages show Monday at First Avenue was packed with fans who were more into “Power Rangers” than power chords the last time the band came to town.

The influential psychedelic folk-rockers from Athens, Ga., went nearly 15 years between tours, in which time collegiate musicheads developed a cultish devotion for the band’s 1998 album, “In the Aeroplane Over the Sea.” A legend also developed around reclusive singer Jeff Mangum, who retreated from the stage in 1998 and didn’t return until a 2012 acoustic tour.

While Mangum’s solo show at the State Theatre that year was more holy and reverential in tone — and actually just a tad more spectacular — Monday’s gig reiterated that NMH is a real band, and a relatively raucous and rowdy one at that. Mangum’s nightmarish-fantasy songs even proved surprisingly fun with the full group in tow. Never mind the lyrical references to Nazis and the Holocaust.

In his Monday return, Mangum looked way more like a recluse, with a thick beard, stringy long hair and a ratty wool sweater. Ah, the old whale-hunter look.

After opening solo with a hyper-strummed “Two Headed Boy,” Mangum’s bandmates joined him for a seamless segue into “The Fool.” The set list followed a similar pattern, with songs bleeding into each other like suites and the musicians changing instruments frequently without stopping.

Julian Koster proved the most dexterous, changing from bass to accordion to banjo to musical saw during the montage of “A Baby for Pree,” “Gardenhead/Leave Me Alone,” all from the band’s only other album, 1996’s “On Avery Island.” The band also pulled from a couple of EPs, with 1994’s “Ruby Bulbs” and “Snow Song, Pt. 1” providing a climactic pre-encore finale.

The concert still hinged precipitously on the “In the Aeroplane” material, which didn’t disappoint. Mangum sang the acoustic epic “Oh Comely” with impressive force, pushing his pained, high-nasal voice to the edge, where non-fans would wince and the die-hards swoon. “Holland, 1945” and “King of the Carrot Flowers (Pts. 1-3)” also came to life magically with the band’s spirited, nearly gushing arrangements.

While fans shouted out ga-ga messages to Mangum between songs — the best might’ve been a simple “I’m happy!” — the singer only responded with timid smiles and thank-yous. Koster thanked all the fans who “stood in line in the freezing cold to be down front.”

As if Minnesota fans would let a -15 windchill spoil their enthusiasm for a concert they waited 15 years to see.