Two important questions about the "smaller, lightweight" one-
Is it DC or AC - and is it the same as the Sony one.
What power rating is it, compared to the Sony one (how many amps?)
The Sony one may actually be a stabilised power supply (I don't know actually) - whereas others could be unregulated and unstabilised.
Be vert, very, careful - if your laptop is damaged, it won't be covered by the warranty.