I run a Dell Inspiron 8000 through a docking station...
the "AC wall adapter" outputs email@example.com. I bought a cheap dc-dc laptop adapter on ebay (specifically, this model). it outputs firstname.lastname@example.org, which is the exact same rating as the OEM wall adapter. I tested the output voltage and it was dead on 20vdc both with and without a load.
It works great, I've been using it for months. it charges an almost dead battery in less than 1 hour while using the laptop (in the docking station) so it seems to have plenty of power. it does however get extremely hot (hot enough to burn your hand on, I was surprised the plastic didn't melt). I removed it from the plastic housing and mounted it in an old ATX PSU case instead. this allows it to run much much cooler (the exhaust fan sucks out the heat). I think it will work for years this way, but it probably wouldn't last too long if I left it in the plastic case (the parts inside can only handle that intense heat for so long). plus I don't want to find out what that PSU will do when it finally craps out
I don't think it really matters whether you're using a docking station or not. I don't think a docking station uses enough power to put a significant drain on the PSU/battery.
In my case, the car adapter's output specs matched my OEM wall adapter perfectly, but in your case the specs are different, so it may or may not work. the only way to find out is to try it. good luck