I guess because batteries while being great for high current operations, are not the most environmentally friendly solution. My DIY power amp requires a +/- 20-

I guess because batteries while being great for high current operations, are not the most environmentally friendly solution. My DIY power amp requires a +/- 20-40V power supply. That would be quite a lot of batteries. Toroidal transformers are the next best choice, since they are smaller than comparable regular transformers. Large caps are not only for smoothing but also act as power bank for instantious large current needs.