{ "background": "Diagnostic systems for power-distribution equipment are promoted to enhance grid reliability, yet robust field evidence of their cost-effectiveness in sub-Saharan African contexts is scarce. Previous studies, often based on modelled data or controlled environments, lack validation through randomised field trials.", "purpose and objectives": "This study replicates and extends a prior methodological evaluation by implementing a randomised field trial to empirically measure the cost-effectiveness of a transformer health diagnostics system within an operational utility in Kenya. The primary objective is to determine whether the diagnostic intervention reduces the total cost of ownership per distribution transformer.", "methodology": "A randomised controlled trial was conducted where 400 distribution transformers were randomly assigned to treatment (diagnostics installed) and control groups. Cost-effectiveness was evaluated over an operational period using a generalised linear model: $\\log(Ci) = \\beta0 + \\beta1 Ti + \\mathbf{X}i\\boldsymbol{\\beta} + \\epsiloni$, where $Ci$ is total cost, $Ti$ is the treatment indicator, and $\\mathbf{X}_i$ is a vector of covariates. Inference was based on robust standard errors.", "findings": "The diagnostic intervention reduced the mean total cost of ownership by approximately 18% (95% CI: 12% to 24%). This reduction was primarily driven by a 35% decrease in unplanned repair costs and a significant reduction in catastrophic failure rates.", "conclusion": "The replication confirms that implementing transformer diagnostics in this context is a cost-effective strategy for improving asset management. The results are robust to the randomised field trial methodology, providing stronger causal evidence than prior observational studies.", "recommendations": "Utilities in similar regional contexts should consider integrating targeted diagnostic systems into their maintenance programmes. Further research should investigate the scalability and long-term sustainability of such interventions across different network architectures.", "key words": "power distribution, asset management, randomised controlled trial, cost-benefit analysis, sub-Saharan Africa, reliability engineering", "contribution statement