Is money earned from increasing the price of goods offered to the manager, or from a percentage from the supplier, considered unlawful, whether the manager knows or not, in the event that procuring goods is not among the basic duties of the job?

There is no objection to an employee working for himself outside of official working hours and taking money for it, provided that the work is not part of his primary job. However, it must be noted that this money is a commission ( جعلة - ju'alah) and it is not permissible to take it without the knowledge of the payer. This condition is not met in the first case mentioned by the questioner, but it is met in the second case. Therefore, one should restrict oneself to the second case, or inform the manager about the first case if one wishes to deal with it.