As he closes in on the Republican presidential nomination, President Trump made a highly unusual stop Saturday, hawking new Trump-branded sneakers at “Sneaker Con,” a gathering that bills itself as the “The Greatest Sneaker Show on Earth.”

Mr. Trump was met with loud boos as well as cheers at the Philadelphia Convention Center as he introduced what he called the first official Trump footwear.

The shoes, shiny gold high tops with an American flag detail on the back, are being sold as “Never Surrender High-Tops” for $399 on a new website that also sells other Trump-branded shoes and “Victory47” cologne and perfume for $99 a bottle. Mr. Trump would be the 47th president if elected again.

The website says it has no connection to Mr. Trump’s campaign, though Trump campaign officials promoted the appearance in online posts.

The unannounced launch came a day after a judge in New York ordered Mr. Trump and his company to pay a whopping $355 million in penalties, finding that the former president lied about his wealth for years, scheming to dupe banks, insurers and others by inflating his wealth on financial statements.

The penalty came after Mr. Trump was ordered to pay an additional $83.3 million to the writer E. Jean Carroll for damaging her reputation after she accused him of sexual assault. With interest payments, Mr. Trump’s legal debts might now exceed a half-billion dollars — an amount it is unclear he can afford to pay.

Mr. Trump’s appearance was met with clashing boos from his detractors and chants of “USA!” from supporters who arrived at the sneaker event decked out in Trump gear. The dueling chants made it difficult, at times, to hear Mr. Trump speak.

Some had been given signs that read “SNEAKERHEADS LOVE TRUMP.”

“There’s a lot of emotion in this room,” Mr. Trump said of the reaction, after holding up and showing off a pair of gold shoes, then placing one on each side of his podium.

“This is something that I’ve been talking about for 12 years, 13 years. And I think it’s going to be a big success,” he said.

As he spoke, the smell of weed occasionally wafted through the room.

Some of those who attended said they were unaware Mr. Trump would be there, and continued to shop as a crowd gathered around the stage. Many in the audience said they were not from the city and instead hailed from nearby states and Washington, D.C.

The attendees skewed younger and more diverse than Mr. Trump’s usual rally crowds. Mr. Trump’s campaign is hoping he will be able to win over more young and minority voters, particularly young Black men, in a likely rematch against President Biden in November.

This isn’t the first money-making venture Mr. Trump has announced since launching his third campaign for the White House in 2022. Mr. Trump last year reported making between $100,000 and $1 million from a series of digital trading cards that portrayed him, through photo editing, in a series of cartoon-like images, including as an astronaut, a cowboy and a superhero. He has also released books featuring photos of his time in office and letters written to him through the years.

Before he ran for office, Mr. Trump hawked everything from steaks to vodka to a venture he called “Trump University.”

The new sneaker website says it is run by CIC Ventures LLC, a company that Mr. Trump reported owning in his 2023 financial disclosure. The website states the new venture “is not political and has nothing to do with any political campaign.”

Still, it describes the sneakers as a limited-edition, numbered “true collector’s item” that is “Bold, gold, and tough, just like President Trump.”

“The Never Surrender sneakers are your rally cry in shoe form,” the description reads. “Lace-up and step out ready to conquer.”

A Trump spokesman did not respond to questions about the event, including whether Mr. Trump was paid to attend.

Among those in the crowd were Jonathen Santiago, 21, and Danea Mitchell, 20, Trump supporters who drove from Monroe County in the northeastern part of the state for the sneaker event. They said they were excited to see the former president and praised how he interacted with the crowd. They also had kind words for the sneakers.

“The red bottoms were a really nice touch,” Ms. Mitchell said.

She shrugged when asked about Mr. Trump’s legal troubles. “I think it’ll be an interesting four years if he’s found guilty, but I have no doubt he’ll be president,” she said.

Also in attendance was a group of “cheer moms” from New Jersey who said they were in town for a cheerleading event and decided to stop by for a chance to see Mr. Trump.

Karla Burke, 48, said she heard some people booing and making noise, but that most people around her had been supporters. “At the front was a different vibe,” she said.

As for Friday’s penalty in Mr. Trump’s civil fraud trial, Ms. Burke said it doesn’t change her support. “I think it was unfair,” she said. “They’re just going after him so he’s not the Republican candidate.”

Mr. Trump flew from Philadelphia to Michigan, where he held a rally in the suburbs of Detroit and railed against Friday’s judgment, which he has vowed to appeal. Both Pennsylvania and Michigan are expected to be critical battleground states.