Power transformers are among the most critical components of electrical power systems, ensuring reliable transmission and distribution of electrical energy. The technical condition of transformers directly affects the reliability, efficiency, and operational safety of power networks. This paper investigates modern methods for assessing the technical condition and diagnosing power transformers. Particular attention is paid to Dissolved Gas Analysis (DGA), thermal imaging diagnostics, partial discharge monitoring, insulation condition assessment, and online monitoring systems. Experimental data obtained from several transformers are analyzed to evaluate their operational status and identify potential defects. The results demonstrate that comprehensive diagnostic approaches significantly improve fault detection accuracy, reduce maintenance costs, and extend transformer service life. The proposed condition assessment methodology can be effectively applied in modern smart grid environments and predictive maintenance systems.