It sounds like you bought two JVC products from different product lines that are not immediately compatible with the supplied cords, but could probably be made to work with a little extra cost on your part for an adapter cable. But you seem to feel that Best Buy should eat the $200 cost of your purchase 8 months down the road, despite the fact that it was your mistake and you agreed by shopping with them to their very reasonable (IMO) 30-day return policy? I just don't see how you could possibly feel that Best Buy is at fault here, or deserving of a rant.
Some extra words of advice to those who shop in big box electronics stores: If you go to a place like Best Buy to buy something, you absolutely MUST know EXACTLY what you want before you go into the store. 99 of 100 people that work at these stores are minimum-wage college kids who don't know jack about the products they are selling apart from what is self-evident at a momentary glance (like whether a camera takes SD or CF). If you ask them if A is compatible with B, you will get "yeah, probably. it should work" because the employees have no accountability, don't give 2 sh!ts about you the moment you're out the door, and they know you can just return the next day** it if it doesn't work.
**This brings up another important point. If you buy any piece of electronics gear, you should get it out of the box and tested within the return period, and certainly within the warranty period. Most stuff has a 1-year *parts only* warranty, and only 90 days labor in the fine print. That means if your brand new camcorder is defective right out of the box but you wait 91 days to find this out, you could be responsible for all the labor cost to fix it! When I worked in this business a decade ago, I would tell my customers, "buy it, but try it!" Some stuff is D.O.A. because electronics are mass produced, shipped long distances and not every unit gets QA tested (or even turned on).
Extended warranties: I know why the store employees and their families recommend them, it's because stores like Best Buy, Circuit city and Sears will usually swap a product for a new one if they see you bought the warranty, rather than service it. If you don't have the extended warranty, you will usually get the 800 number of the manufacturer's service center from the store, and no further interest in your case (not their problem). Even one repair on something like a high-end camera can be the cost of the service plan just in labor. That's what the salesmen will tell you when they pitch you the ESP, but it's often true. All insurance policies are a form of gambling, and these ESPs are no exception. Cost of the plan is directly linked to how often they are claimed. If you've got kids, or butterfingers, it may well be worth your while to get the extended service plan. If you're careful with your gear, it may not be worth the cost. Manufacturer's defects usually show up quickly (the infant mortality issue), but most extended service plan issues are about breakage or wear of parts due to normal usage.