The moon's albedo is around 0.1, meaning it reflects about 10% of the sunlight that hits it, for a peak illuminance of a few tenths of a lux (sources on albedo and lux). Even if the moon were a perfect mirror, it would only reflect 10x as much light and would only cast a few lux, making its illuminance during a full moon only a few hundredths of a percent of the sun. A perfect mirror supermoon would barely qualify as emergency lighting, which is normally a few lux. Under the absolute best conditions, a completely reflective moon would have about a third of the illuminance of a typical streetlamp. On average, it will be less than a tenth of a typical streetlamp, making it rather unsuitable as a replacement for electric lights.
Talcum powder will increase the albedo of the moon, but certainly not as much as a mirror finish, so the effect will be extremely modest at best. No amount of increase in the moon's albedo will make it a viable night-time illumination source that can replace electric lighting on its own, as it will never be as bright as a regular street lamp, which is normally 10 lux. 580
Increasing the albedo of the moon will help you see better during the night, but for almost any application where you already have night-time illumination (streets, sidewalks, outdoor events, etc.), you'll still need illumination even with a 10x as bright moon. The electricity savings will be small, since there is very little external lighting that becomes unnecessary with a brighter moon (although I suppose you could turn all the electric lights down a few percent if the moon makes up the difference).
EDIT: To summarize the comment chain below, I'm not in any way arguing that the moon is not or could not be a useful illumination source at night. But it will never replace electric lighting, as its illuminance is far below that of electric lights. At best, the moon could produce about 10% of the lighting level that is deemed useful and appropriate for the general public in day-to-day life. Since we're talking about a society that is engaging in planetary-scale projects, I think it's safe to assume its citizens need night-time lighting for more than not tripping over things in the dark (which can be done at mere thousandths of a lux, no moon alterations needed). Anything that requires moderate visual acuity, like making out text or faces or objects quickly or at a distance or while moving will be difficult by moonlight no matter how shiny the moon is. 840