The UPS system is the iron lung that keeps the data centre going when it's in need of the coronary heart team. It's the last place I'd be looking to save money!
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In general the addition of capacitive and inductive filtering elements can definately increase conversion efficiency.
More appropritely use a Switching-type, since in this case all of the input waveform represrents "usable" power. A switching regulator would compensate for the ripple-voltage component of the waveform - not by dissipating it, but by varying the pulse rate or pulse duration to convert the ripple voltage into usable output power. For the fluctuations in ac line voltage it varies its pulse rate or pulse duration to compensate for such fluctuations.
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