ubw, I can see the problem is that the output socket is soldered directly to the regulator board, so putting diodes in there is not a straightforward mod. It seems that if we want to maintain an accurate voltage display then some major surgery will be required. Another option is to replace the pot. From the LM317 circuits I have seen, it seems that the output voltage increases with increasing resistance in the pot, so theoretically using a lower value pot should limit the maximum voltage. We would need to know the resistance of the existing pot and take a guess at a suitable replacement value. I've been working on a variable power supply design but making something that is efficient and cost effective is more difficult than it first appears. Funnily enough it is the housing, sockets, switches and other hardware that start to bump up the cost... the kinds of things that the Chinese can do for next to nothing.