In this paper we evaluate the performance of space-time block coding (STBC) with linear combining (LC) decoding in power line channels dominated by asynchronous impulsive noise. Based on the natural signal redundancy provided by the space-time structure, we present a new decoding scheme that shows a significant coding gain over the LC decoder for SNR levels below 18 dB. In addition, we propose a novel adaptive scheme, which combines both detection techniques at the receiver. The performance of the adaptive system is superior to conventional STBC with only LC detection over a wide range of SNR levels.