I am considering building a 'trickle' usb charger for my laptop.?

On dell laptops there is a third wire which ensures a real dell charger is being used. This connection is a common failure point on my model so now, for the second time, while my charger operates the laptop fine, it does not charge. I would think incoming power to the laptop via two USB connections would provide a charge rate of 1 am, hence a 'trckle' charge. Is this possible? And if so could anyone provide tips.