<p>Transcranial electrical stimulation (tES) is often used in clinical practice as an adjunct therapy. However, the impact of combining different methods on the overall effectiveness of therapy and the relative effectiveness of tES compared to other therapeutic approaches remains unclear. A search of the PubMed database was conducted up to April 4, 2025, and a systematic review of study results was conducted according to the PRISMA criteria. The primary search included articles addressing the treatment of mental disorders with various types of tES as part of combination therapy or in comparison with psychopharmacological medications, psychotherapy, and cognitive training. A total of 1,689 publications were retrieved, 46 of which were included in the review. Anodal tDCS of the left dorsolateral prefrontal cortex (dlPFC) remains the most studied tES method. Its effectiveness for depression appears to be comparable to that of antidepressants at intermediate therapeutic doses. Augmentation of anodal tDCS of the left dlPFC with antidepressant therapy, but not cognitive behavioral therapy, also demonstrated an advantage over monotherapy in non-resistant depression. Anodal tDCS of the left dlPFC in combination with cognitive training in mild cognitive impairment is probably more effective than monotherapy with only one of the methods. Studies of some disorders and other types of tES remain sporadic. Small cohort size is a limitation of many studies. Thus, tES appears to be a promising therapeutic approach that may find its place in the treatment of mental disorders; however, further research on a variety of tES approaches is needed both in different disorders and in different combinations with other treatment methods.</p>