Some things I collect avidly and with great pleasure, like detective stories. Others I accumulate reluctantly and with increasing distaste, like power supplies. As with most twenty-first century households, we have an ever-growing collection of power supplies for various devices which have broken, been stolen or simply retired from old age. ‘I’ll keep the power supply!’ I think. ‘It may work for something else!’ But it seldom does. Each new manufacturer feels duty-bound to require some new combination of voltage and jack size which renders every previous power supply totally useless. I recently acquired a new ten-inch Android tablet as part of...