Usb data and power

Hello, i'm new to this and hope someone can help me. I have a project with a power supply and a gps. The gps (china one) came with a usb to mini-usb cable to transfer files and charge it. We removed the batery from the gps and we are using only the power supply to work with it. The power supply (5v) provides power to the gps. Gps turns on and works just fine. On the data side. We modded the cable that came with the gps to work with our power supply. We cut the cable and remove both power cables going to the computer, then attached the 2 power cables from the power supply to the mini-usb but we leave the 2 data cables intact. The problem is we are no longer able to talk to the device with that cable. We tested the cable on an external dvd drive and worked as we power it on and read a disc with it, so don't know if it's different with the gps. Does anyone has a clue on this?

i dont know any of this stuff but other members may find it easier if u linked a page about your gps model i posted this so that it may save your time

this is the unit