The new generation of uninterrupted power supply is UPS, working in On-Line mode with delta conversion technology. This technology is developed and is patented by Silicon company (Denmark). The realization of this technology in DP300E Silcon U P S allows to minimize or completely remove such disadvantages, of traditional 3-phase double conversion UPS, as: low efficiency due to double conversion, low input PF, high level of harmonics fed back to mains due to unlinear input current and others. In this article there is a comparison of technical and economic properties of delta conversion and double conversion UPS, and principles of delta conversion and notable features of new technology.