A preferential margin of up to 15%, or any other preference, may be accorded to "national providers" (i.e. entities majority owned by South Sudanese persons)  or domestically produced suppliers in public procurement proceedings, if authorised or required by regulations enacted under the Public Procurement and Disposal of Assets Act.
"Section 5: intepretations
In this Act, unless the context otherwise requires:  [...]
"Foreign Provider" means a Provider or Contractor whose business is not registered in South Sudan;
"National Provider" means a Provider or Contractor registered in South Sudan and owns majority shares by South Sudanese; 
[...]
CHAPTER IV: Basic Public Procurement and Disposal of Assets Rules [...]
Section 38: Participation by Providers and Contractors
(1) Candidates shall participate in procurement proceedings without discrimination except where participation is limited in accordance with this Act and the regulations;
(2) Subject to sub-section one (1) above the Minister shall in consideration of economic and social development factors, prescribe preferences and or reservations in public procurement and disposal of assets;
(3) The preferences and reservations referred to in sub-section (2) shall: i. be non-discriminatory in respect of the targeted groups;
ii. allow competition among the eligible providers or contractor's;
iii., be monitored and evaluated;
iv. works, services and goods, or any combination thereof,
v. identified regions; and
vi. such other categories as may be prescribed.
(4) The preferences and reservations shall apply to;
i. persons such as disadvantaged groups, Small and medium enterprises;
ii. women, youth and people with disabilities,
(5) Applying the preferences and reservations under this section,
i. exclusive preferences shall be given to citizens of South Sudan if the funding is 100% from the government of South Sudan;
ii. the amounts are below the prescribed threshold; and
a prescribed margin of preference may be given in the evaluation of bids to candidates offering manufactured goods, mining, and extraction grown in South Sudan.
[...]
Section 41: Evaluation Criteria and Procedures
(1) The evaluation criteria relating to the subject matter of the Public Procurement and Disposal of Assets Process shall include:
(a) price;
(b) the cost of operating, maintaining and repairing Supplies or construction, the time for delivery of Services, completion of construction or provision of Services, the characteristics of the subject matter of Public Procurement and Disposal of Assets Process, such as the functional characteristics of Services or construction and the environmental characteristics of the subject matter, the terms of payment and of guarantees in respect of the subject matter of the Public Procurement and Disposal of Assets Process;
(c) where relevant in Public Procurement Processes conducted in accordance with this Act, the experience, reliability and professional and managerial competence of the Provider or Contractor and of the personnel to be involved in providing the subject matter of the Procurement Process.
(2) In addition to the criteria set out in sub-section(1) above, the evaluation criteria may include:
(a) criteria that the regulations made under this Act or other provisions lof the laws of South Sudan authorise or require to be taken into account; or
(b) a margin of preference for the benefit of National Providers or domestically produced Supplies, or any other preference, if:
(i) authorised or required by the regulations made under this Act or other provisions of applicable law;
(ii) such margin of preference has been calculated in accordance with the regulations made under this Act, but in no case should exceed fifteen percent 15%. [...]" (Public Procurement and Disposal of Assets Act, 2018, Section 41)
Public Procurement and Disposal of Assets Act, 2018
[<a href="https://mofp.gov.ss/laws/PublicProcurementandDissposalofAssetsAct2018.pdf">Act</a>]