I recently bought the delta stem extender to raise my headset. The stem now wiggles. I follow the instructions and all the bolts are tight. Not sure if it has to do with spacers?

Need more info. Picture would be most helpful.

Could be taht the extender doesn't fit as far onto the steerer as the stem did. Si it bottoms out of the top end of the steerer before the headset is drawn up tight. Spacers. Andy.

Or maybe you have a 21.1 mm extender and a 22.2 mm steerer tube.

If the stem wiggles, either it's loose on the extender, or the extender is loose on the steerer tube.

OR, you haven't assembled it correctly and the headset is loose.

First diagnose for a loose headset, by applying the front brake and rocking the bike forward and back against the front wheel. If you can see or feel any play, (usually most obvious at the lower bearing). you have a loose headset. That's corrected, via spacers under the extender, and the top cap screw the same way it would be without the extender.

OTOH if the headset is OK, make sure the extender is engaged on the steerer close to, but not bottomed it's full depth.

The most common mistake, is to have the steerer bottom (top) out inside the extender, which will make HS adjustment impossible. You want maximum engagement, short of bottoming, so that the extender pushers the spacers outside of the steerer and can compress the headet bearing stack.