Instruction: Parse the product information to locate the target attribute, and then provide the extracted value of the target attribute and its source in the output, specifying None if the attribute is not present.

Input:
Product title: Laptop Notebook Charger for Lenovo ThinkPad X61 X61 X61 7762 X61 7764 X61 7767 Adapter Adaptor Power Supply (Power Cord Included)
Product description: Lenovo Replacement Laptop Charger - US Power Cord Included - Output: 20V 4.5A 90W
Product feature: Replacement Laptop Charger, US Power Cord Included, Input: 100-240V, Output: 20V 4.5A 90W
Product brand: Lenovo
Target attributes: Maximum Output
Answer: attribute: maximum output
value: 20v
source: product feature
attribute: maximum output
value: 20v
source: product description