I encourage you to talk to him and be frank with him. I am bumping up Wellbutrin to the max [450mg per day] after years of treading water on 300mg a day and no add-ons. The reason being I've been sliding lately and feeling worse more often. Adding a mood stabilizer was recently suggested to me but I decided to try the max dose first. My doc was ok with me trying that first.
Seems your Doc wants to try that same max-dose route first. If bumping up the Wellbutrin doesn't have the required effect for you then he'll likely want to go the add-on route. The only thing is, you have to give the Wellbutrin increase a good couple of months or so to see if it's acceptably effective for you. A good thing to realize is that most psy-docs will prescribe diff med/s if one isn't working. They have a responsibility to find you the most effective med/s for your situation. There are many meds available and the reason there ARE so many is because what works well for one may not for another.
I suggest asking him for a brief visit to talk about your situation and bring up the question about what might happen if the dose increase isn't effective. Ask him about add-ons and is that a route he would consider. He'll likely say yes and that knowledge should ease your concern a bit while you're waiting the 8 weeks or so to see if the anti-dep increase is effective.
I hope that's making sense and a bit of a help. Hey, and welcome to msf. It's a pretty big place and there's a lot of resources + ways to be involved on whatever level you like. The mods here are great and run a pretty safe ship. I'll check back here later. I hope you're doing ok.