Our sources say Mayweather was leaving the downtown L.A. Ritz last night -- headed down the block to Crypto.com Arena for game 5 -- when he saw several men on the street.

We're told Mayweather began talking to the guys, and decided he wanted to help ... so he busted out his backpack, and blessed each guy with 10 racks.

"I don't want to show my face, but [Floyd] just gave us $30,000," Reynolds, one of the men, said after receiving the gift.

The guys didn't want any photographs released, fearing they'd be targeted for carrying the cash.

"We do not want to get robbed. We will go find a motel."

FYI, California has the largest homeless population in America ... with U.S. government data indicating there are over 180K unhoused people in the state. The country, as a whole, has around ~650K experiencing homelessness.

We're told the hope is the money can get the guys on their feet, allowing them to improve their situation.

Floyd's charity didn't end with the guys he met outside the luxury hotel ... the 50-0 fighter also hooked up a few kids with $500 who were selling candy outside.

Mayweather ultimately made it to his courtside seats where he watched the Luca Doncic-led Mavs handle the Clippers, 123-93, taking a 3 games to 2 lead in the first round series.

Doncic, who is dealing with multiple ailments, including sickness and injury, had a tremendous game, dropping 35 points, 7 rebounds, and 10 assists in the win.