Provided are a method in which a first device performs wireless communication, and a device supporting same. The method can comprise the steps of: deciding first power for physical sidelink shared channel (PSSCH) transmission in a second symbol duration; deciding second power for physical sidelink control channel (PSCCH) transmission in a first symbol interval on the basis of the first power; performing the PSCCH transmission to a second device in the first symbol duration on the basis of the second power; and performing the PSSCH transmission to the second device in the second symbol duration on the basis of the first power. The second symbol duration can comprise resources for the PSSCH transmission. The first symbol duration can comprise resources for the PSCCH transmission and the PSSCH transmission.