The white powder that often appears on the leaves of the jade plant is usually either from a salty solution that is excreted from the plant, or it is a white fungus that develops on the leaves from improper care.
How to tell the difference:
If you see any areas where the white powder appears to be in the form of small circles, then this might indicate that it is fungal growth and not your plant excreting excess salts.
Some plants, such as the jade plant, will actually excrete excess salts that it has absorbed out onto its leaves as a means of ridding itself from it. This might be caused by excess salts in the soil or in the water it absorbed. Your jade plant is well equipped to handle this though and will get rid of these salts by excreting them onto its leaves. The liquid it excretes will evaporate leaving just the white powdery salts behind.
If this is the case, just make sure you have quality soil and water that is not high in salinity. Then you can use a soft damp cloth to wipe the leaves clean. Even if your water and soil are ideal, your plant might still excrete this substance, and that is completely alright. Just wipe the plant's leaves from time to time, and it should be fine.
The white powder on the leaves can also be a fungus that is starting to grow due to excess humidity, low light conditions, and cooler temperatures. This fungus is most common in the cool winter months.
If this is the case, take care not to get the leaves damp during watering of the plant. Also, consider increasing light exposure or even utilizing a fan to increase air circulation. This will also help to keep the leaves dry and inhibit fungal growth.
You can remove any shoots or leaves of the plant that are heavily affected and treat any other's with a light misting of a baking soda solution. For the baking soda solution, mix four teaspoons of baking soda to one gallon of water. Ensure the water is room temperature or slightly warm. Then use a spray bottle to mist the plant lightly. Do this daily until the problem is corrected.