Zak Bagans -- I Scored Michael Jackson's Propofol Chair!

Zak Bagans just added to his creepy collection of memorabilia and bought Michael Jackson's old chair ... from his death room.

The chair was decor in MJ's Holmby Hills mansion ... and primarily used by Dr. Murray to monitor the singer when he was pumped full of Propofol.

The "Ghost Adventures" star tells TMZ he scored the seat for around $15k ... and plans to put it in his Las Vegas Haunted Museum, along with Dr. Kevorkian's van and his body part cauldron.

Zak also wants Dr. Murray to come to Vegas and talk about the chair in person -- and considering the good doc's history with strip clubs -- that might not be out of the question.