i think you shoukd try a usb hub.
I would like to use Windows Tablet for my Car PC.
I have a good one but it just has one USB port for power and USB accessories such as flash drive, GPS receiver,...
How can I use just one USB port that the tablet has to charge the tablet and plugin GPS receiver at the same time? I meant charging and receiving GPS signals at the same time with one USB port that the tablet has.
I am assuming you mean it has a mini or micro USB port similar to most smart phones and not a standard USB socket to plug things like a mouse into.
Assuming this is the case look for an on the go cable... They will be called an OTG cable.To also charge your tablet you want an OTG charging cable. This assumes your tablet will support charging while being used as a host.
Most of the latest Android tablets and phones support this so hopefully your PC does.