Hi,
The FW13/16 laptop can have difficulty powering on with a low watt psu. E.g. 25W
When you first plug in the psu, the EC negotiates a SRP of 3A, 5V. When you press the power button it starts booting, but at the same time negotiates up to 2.7A, 9V (25W). If the new level is SRP, the usb standard states that as the Amps reduce. The transition has to go via 0.5A, 5V. (2.5W). 2.5W is not enough to boot the laptop so it fails.
If the psu is in the SPR at say 5A,20V (100W) and it wishes to switch to EPR 5A, 36V (180W). It does not need to go via 2.5W that the BIOS is currently doing. It should first switch from SPR to EPR still at 5A,20V. The progress up smoothly to 36V.
The problem is progressing between levels while staying in SPR mode. The solution is switching to EPR mode and progressing there.
So, from the top example, if the EC switched from 3A, 5V SPR to 3A, 5V EPR. It could then progress up to 9V without going via 2.5W.
Another option would be the EC to switch to 9V first, and only then, start booting.