A Universal Serial Bus (USB) to Serial ATA (SATA) bridge device and method for operating same in a USB connected mass storage subsystem supports software management of power consumption. The USB to SATA bridge estimates power consumption based on known power consumption characteristics of SATA disk drives when performing commands involved in accessing SATA drive, or takes measurements of power consumption during execution of commands to determine when responses to a USB host device are to be delayed. By selectively delaying responses to the USB host device issuing the commands, the USB to SATA bridge manages the rate at which the host issues commands to the USB mass storage subsystem and is thereby able to automatically limit power consumption of the USB mass storage subsystem to that that available over the USB link.