The AirCheck G2 has two USB Type A ports on the right side of the test unit. The bottom one (Port #1) is fully USB 2.0 compliant port which can supply a maximum of 500mA. The upper one (Port #3) is similar but can only supply a maximum of 200mA. Most USB thumb drives will operate properly in either of the two ports since power consumption is typically low for storage devices. However, some of the newer, USB 3.0 thumb drives are quite large and therefore consume more power. Even though these higher power USB 3.0 drives can communicate on USB 2.0 ports like those on AirCheck G2, their power consumption may be too high for proper operation. There have been some instances where a newer USB 3.0 drive requires more power than 200mA, which is the maximum that can be supplied on Port #3. In these situations, use Port #1 (lower port) which can supply 500mA. In very rare situations, even 500mA may not be enough current to support a connected USB device and therefore, a lower power device needs to be used for connectivity/storage.