Alternator upgrade?

[Anonymous]

I have a standard 1.2i alternator, and need to know at what point will this need upgrading. I have installed a digi-dash, electric windows, alarm, in car neons, central locking, heated seats, stereo and soon a 400w amp and a sub. Will i need to upgrade my alternator (as my local mechanic suggested), and if so what would be the best alternator to replace it with and roughly how much would this be?
Thanks

[Anonymous]

I replace my GTE cos it was not charging with an identicle item ?10. so what i'm saying is an easy upgrade would be the GTE for a tenna.