Samsung Galaxy S9 and S9+ Smartphones: Super Slow-Mo Video, Low Light Camera, AR Emoji, IP68 Water & Dust Resistance, Expandable Memory of Up to 400GB with a Micro SD Card, Smartphone Protection
SanDisk 400GB microSDXC UHS-I Memory Card for Nintendo Switch SDSQXAO-400G-ANCZN - Best Buy
Here are the best microSD cards for the Samsung Galaxy S9 & S9+
Amazon.com: SanDisk Ultra 400GB MicroSD XC Class 10 A1 UHS-1 Mobile Memory Card up to 100MB/s Read Speed (SDSQUAR-400G-GN6MN) with Mini MemoryMarket MicroSD Memory Card Reader : Electronics