Would agree with vapour, the 1060 6GB is the best one to get atm if you're buying used. The RX 580 is about the same, better in some games, worse in others but the pricing on that gpu is highly inflated due to crypto-mining. Not saying that the 1060 isn't overpriced at the moment but it is overpriced less. Make sure you have the PSU to back up the GPU.
I looked up the Inspiron 3650 and I saw that there was a small form factor one too. If you have that one, you would be better of buying a 1050 ti because there are some great half sized ones. Looking for a used graphics card can also be good because you might get better or around the same performance for the same amount, for example a GTX 980 instead of a GTX 1060 because it delivers the same performance but you can often find it for way less.