Good old sugar
To be perfectly honest the best way (in my opinion) to sweeten wine is using ordinary white granulated sugar and the amount I recommend is 150g per demijohn (5 litres). Try a few experiments of your own with different amounts, and once you find your sweetness level, stick to it.
I sweeten my wine when I’m sure that all fermentation is complete and add the sugar as a syrup adding the desired amount of sugar to boiling water and allowing to cool before adding to a racked demijon of wine I then leave the wine in a warm place, just to be sure fermentation doesn’t start again. I then move it to cool position to fully clear, then bottle and enjoy.
There are many natural and artificial non-fermenting sweeteners that can be used when your wine isn’t as sweet as you would like. Each one has pros and cons but in the end, it comes down to personal preference or availability. As long as they are non fermenting, the aim of sweetening homemade wine can be achieved. Or you can use the safe option of the Youngs Wine Sweetener which is made to do the job
The other option of artificial sweeteners are listed below. Why not experiment with any of the wine sweetners below.