Negative supply should be distinguished from low-grade or fake supply.
Low-grade narcissistic supply comes from sources which cannot be idealized, no matter how hard the narcissist tries and to what extent he blocks out and denies reality. The type of narcissistic supply determines whether its source can be idealized or not. For instance: compliments on his intellectual achievements doled out to a cerebral narcissist by an intellectually-challenged person would never pass muster and would never qualify as narcissistic supply.
Fake narcissistic supply is tinged with ulterior motives and hidden agendas. Sources of fake supply compliment the narcissist in order to manipulate him or some third person or in order to accomplish a goal. Endowed with cold empathy, the narcissist picks up on these true motivations and feels injured and slighted. Many narcissists test their sources of supply repeatedly: they engineer situations intended to expose the sincerity or lack thereof of the supply and the consistency and authenticity of the source's conduct.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/the...)