On a Dell E6510 laptop, there are 4 ports: 3 USB, and 1 eSata. The ports on the left side of the laptop are USB and eSata. Both of these ports start losing voltage after some time of operation, say ....1 hours to 5 hours. I say lose voltage, because I actually hooked up a 5volt DC tiny fan to the usb port (no HD connected to eSata port beneath it. After about 90 minutes, the fan slowed down. I unplugged it and connected it to the usb port on the right side of the laptop and it imnediately resumed it's normal rpm and stayed there until shutdown several hours later. P.S: The voltage drop occurs on both ports on the left. The eSata port also functions as a usb port, and the fan slowed down on it as well. Connecting a sata dist to the eSata port leads to the disk disappearing from /dev when the voltage drops.
Power management is not enabled as laptop is always on AC. Screensaver's power management is configured to never turn off monitor, nor disks nor suspend system ...etc.
So, what might be causing the voltage drop, and how can I prevent it from happening? What data do I need to gather?