Update Table contents from another table
According to Postgres docs (9.6):

UPDATE Products as P
SET P.CategoryCode = T.CategoryCode,
    P.CategoryName = T.CategoryName,
    P.SubcategoryID = T.SubcategoryID,
    P.SubcategoryName = T.SubcategoryName,
    P.BarCode = T.BarCode,
    P.Weight = T.Weight,
    P.ManufacturerSKU = T.ManufacturerSKU,
    P.ProductName = T.ProductName,
    P.WarrantyLength = T.WarrantyLength,
    P.Manufacturer = T.Manufacturer,
    P.DBP = T.DBP,
    P.DBP5 = T.DBP5,
    P.RRP = T.RRP,
    P.StandardRRP = T.StandardRRP,
    P.AvailabilityTotal = T.AvailabilityTotal,
    P.AvailabilityAdelaide = T.AvailabilityAdelaide,
    P.AvailabilityBrisbane = T.AvailabilityBrisbane,
    P.AvailabilitySydney = T.AvailabilitySydney,
    P.AvailabilityMelbourne = T.AvailabilityMelbourne,
    P.AvailabilityPerth = T.AvailabilityPerth,
    P.ImageUrl = T.ImageUrl,
    P.ImageFilename = T.ImageFilename,
    P.DescriptionLink = T.DescriptionLink
FROM tmpprod as T
WHERE P.StockCode = T.StockCode;


Although I used an alias, it is not indispensable.