10. Is there a ban on donations from corporations with government contracts to candidates?

10. (1) No person or entity may deliver a donation to a member of a political party other than for party political purposes. (2) A member of a political party may only receive a donation contemplated in subsection (1) on behalf of the party. (3) No person may circumvent subsections (1) or (2), or any of the provisions of this Chapter.

The Political Party Funding Act 2018 

Independent candidates are currently exempt from the Political Party Funding Act and its regulations (https://www.elections.org.za/pw/FAQ/Political-Party-Funding)