There are contests where a prize is offered to whoever converts the highest Watts in the smallest package, or least parts count, or lowest weight. It probably is hard to beat the best in this field.
What is getting lots of attention is wireless power transfer. Developers would love to find a way to make it more efficient. I read financial reports that claim this or that company is 'about to make a major breakthrough' in wireless charging or wireless power transfer. We would like a method to make it directional yet harmless to humans who are in the path. It's interesting to think about how to solve the challenges, as in what antenna shape, or what frequency range.
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There is a need in some parts of the world for AC mains voltage stabilization (due to overloaded power grids). Each house could use a device to step-up their voltage, and make it adjust the ratio of increase. The solution could be a variac which has no moving parts. Its output shall automatically adjust to 230 VAC, no matter what the input amplitude. This is not easy to achieve, or else it's not cheap, or it's risky for ordinary people to use. Etc. This is an opening for some very clever developer.