Review on Goldsource STU-500W Voltage Transformer Converter: AC 110V/220V Step-Up/Down Power Converter with 5V USB Output, 500 Watt - Efficient Power Transformation Solution by Dave Connelly

I've used these voltage converters in Iraq, Afghanistan and Africa and they've never let me down. Performance seems pretty clean even on unstable mains, although there might be something to be said if you want to hook up some sort of power supply after this converter if you really want clean AC/AC waves. A power surge will blow the fuse, so have a few spares on hand, but I find a blown fuse preferable to a blown unit. I always use a strip of red tape across the 220 jack so I don't accidentally connect something to the higher voltage side of the box. Power surges will cause this voltage converter to pop and sometimes even knock. However, these noises don't seem to translate into output voltage spikes.