Dolvett Quince -- of 'Biggest Loser' fame -- is being dragged to court by his ex-wife ... 'cause she says he owes her a fat stack of cash, and she wants to collect.

According to new legal documents, obtained by TMZ, the famed TV trainer Dolvett's ex, Amanda Quince, claims he's falling way behind on spousal support -- to the tune of 5 figures, in fact. Amanda claims Dolvett is supposed to pay her $2,500 on the first of every month ... but she says the money isn't flowing her way of late.

In the docs, Amanda says Dolvett now owes her $10,000 because of this ... explaining that over the past six months or so, he's only given her $5,000 of the $15,000 he was supposed to shell out.

Amanda claims Dolvett has the money ... she says he's making upwards of $35,000 a month and has no problem shelling out over $8,300 for his Santa Monica penthouse. If he can afford that, she's questioning why he can't cover the money he's allegedly behind on.

Probably worth noting -- Dolvett and Amanda have been divorced since January 2023 ... and she says he's given her hardly any financial support since their marriage ended, this despite the fact that he's supposed to. Amanda claims she's now unemployed and barely scraping by on food stamps. She's asking a court to make him pay her what she says he owes.