It appears you have me at a disadvantage. You sly devil, you knew I'd run headlong into a wall, wink,wink. As indicated above, I used an Igo and solar panels to charge AA & AAA batteries. Small panel, small load. Everything worked according to my evil plan, or so it seemed. As indicated, I wasn't happy waiting all day or two for my batteries to charge and thus I purchased a quicker USB charger , Eneloop, rated at 500 ma. After playing around all day yesterday I've come to the same conclusion you commented on in your USB/ DC /Solar Li/po charger product design document, "instability confuses battery chargers," should have read that before I.... Oh well, it was a learning lesson, and fun too. The little Igo still works but not much better than my original, dumb, little aa & aaa solar lamps, ticks I called them because they're suspended all over me while hiking. Yours is obviously the superior logic. While not an EE I can still read.
Finally my question, drum roll, would it be possible to substitute, obviously with mods, capacitors for the lipo cell in the USB/ DC /Solar Li/po charger design as a pass through to the USB? You've obviously given this problem a lot more time and consideration than I have or ever could. All my research indicates that everyone is looking at the Lipo solution, which is great for obvious reasons, but not in my case, or other hiker's for that matter.