The Quicktake 100/150 uses the same M4662 AC Adapter as the Powerbook 165c/180c, I have one here with the box. Its a 24watt power supply 7.5v rated at 3A.
http://www.ebay.com/itm/281102652682
I also have the "Low Power" APS-17adp which is 7.5v rated at 2A. It works fine with my Powerbook 165. I highly doubt its different from the M5651, just a newer revision that came out after the 24w/3A M5652/M4662 adapters hit the scene. The "Low Power" terminology was likely needed after the higher amperage adapter was released to allow customers to identify it from the higher power adapters even though the 3A version had "24w" molded onto the DC jack.
http://www.ebay.com/itm/281102652682
I also have the "Low Power" APS-17adp which is 7.5v rated at 2A. It works fine with my Powerbook 165. I highly doubt its different from the M5651, just a newer revision that came out after the 24w/3A M5652/M4662 adapters hit the scene. The "Low Power" terminology was likely needed after the higher amperage adapter was released to allow customers to identify it from the higher power adapters even though the 3A version had "24w" molded onto the DC jack.