This is a random question, but I was curious what the return policy is generally like at electronics stores in Tokyo.

For example, if I purchase a cheap monitor, take it back to my place, unbox it, and realize it's not compatible with my laptop, will I be able to return it for a full refund to my credit card? If so, within how many days usually?

In the United States, e.g. at a store like Staples, you can generally do this without much of a problem as long as it's within 14 days or so.