Most brewers recommend limiting the use of dextrose to the priming stage of the procedure, as it tends to produce cidery flavours when used in large quantities that are generally undesirable. Some online shops sell dextrose as a 1% alcohol booster kit. No more than perhaps a single pound should be used. If using refined sugars or honey as more than 20% (by weight) of your fermentables, consider adding some yeast nutrients so the yeast are health. Some varieties such as Doppelbocks are near impossible to make with out the use of non-malt sugars, as you can not get the alcoholic strength and light body through all-malt.