Tracy Chapman has blown a fuse. She stands in darkness while electricians scurry around to fix the problem. Suddenly, taking an acoustic guitar, she stands without a spotlight and launches into the Animals' House of the Rising Sun. It seems an unlikely cover until the significance of the words hits home - "There is a house in New Orleans ..." Chapman has turned an awkward personal moment into a comment on a natural disaster that has brought crisis and political uprising in America. No wonder everyone in the house is soon bellowing out cries of "Tracy! Tracy!" The hits and million-selling albums are gone now - in the UK, anyway - but the Cleveland, Ohio singer who grew up amid racial segregation retains a large constituency and a strong voice. That voice is unexpectedly powerful live: stark, haunted yet warmly human. Change - from her latest album, Where You Live, in which a lovely melody is allied to the striking words, "If you knew that you would die today ... would you change?" - is stunning.

Chapman has struggled to reinvent the image of her as the acoustic-wielding tender warrior who debuted Fast Car to global impact at the Nelson Mandela concert in the 1980s. Here, she's giving it her best shot. Songs are embellished with bass, drums and echo; there's even a cover of Nirvana's Come As You Are. But her best tune sees the acoustic Chapman of old breaking off to angrily hammer at tom-toms. America is her most direct, striking song since Fast Car, dissecting US imperialism with killer lines like, "Your sons and daughters will never sing your praises while you're conquering, America". As she segues instantly into Talkin' Bout a Revolution ("Poor people gonna rise up ..."), it will take more than blown fuses to stop Tracy Chapman fighting the power.

· At Hammersmith Apollo, London W6, tonight and tomorrow, then touring. Box office: 0870 606 3400.