Android devices don't have enhanced support for USB adapters. There are rumors over Internet that users experienced problems while using high power consumption devices on their Androids like external HDDs and more. However, connecting two external HDDs to an Android device should not be a problem if you are using a version of Android higher than 4.0. If you experience problems, try performing a software update. It's also a good idea to visit the manufacturer's official support website to download any available driver, firmware for your device.