Jermaine Dupri Six Figure Song Request

The rapper was spinning at TRYST nightclub at the Wynn Hotel on Saturday ... when some super rich guy -- known as "Su Su" -- dropped $90k on a 15 liter bottle of Ace of Spade Rose Champagne ... plus an extra $40k on other fancy booze.

Sources tell us club honchos were so thrilled about the purchase, they asked Dupri to give Su Su a special VIP shout out.

Dupri not only obliged ... but he was so impressed with the purchase, he LET THE GUY REQUEST A SONG!! Which -- if you've ever been to Vegas -- never happens.

It gets better ... "Su Su" was so thankful Dupri actually played his tune he stuffed an additional $3,800 cash in his pocket as a tip!