I almost always go with 3rd-party options whenever comparable ones are available: Amazon Basics is a staple around here. There are 3rd-party chargers for the SP2 at amazon, but they are not as compact as the RT/SP2 ones. If I needed one today, I'd go with the original design, but not because it's OEM.
BTW, Best Buy matches advertised prices, including on-line prices -at least from standard stores. My brother bought a nice set of Sennheiser headphones and got an Amazon price, which was $15-20 less. The salesperson went to the website, confirmed the price, and we got it. This was at the local store, and I don't know if this policy or practice varies across stores.