Mean Well is already in China, of course. So the only advantage you gain by doing it yourself is whatever their profit margin is, and it's probably tiny; in return for which, you need to do some engineering, stock a bunch of expensive parts including magnetics, and do a lot of testing. If it were me, I'd be inclined to let Mean Well do the dirty work. After all, you're not planning on rolling your own electrolytics, or mining your own copper, right?