You can use the USB charger with 120 W power for your Xiaomi 15 Ultra. Although the Xiaomi 15 Ultra supports a charging speed of 90 W, the charger is compatible with 120 W and delivers the necessary power without causing problems. The charger has a USB-A port and supports HyperCharge technology, which enables fast and safe charging. So you don't need another charger that has exactly 90 W, as the 120 W charger works without any problems.