Review on Top-Rated BESTEK 400W Car Power Inverter: DC 12V to AC 110V Adapter with 5A 4 USB Charging Ports by Matthew Bahri

To calculate DC power: W = Voltage x Amps To calculate AC power: W = pf x Voltage x Amps Pf for resistive load 1: This is a simple motor Pf for inductive load Average 0.8 electronic loads or inductive motors. So far, so good. I got this, ran to my truck, hooked it up to a 12v outlet and an air pump for a Coleman mattress. Have it on and off. It's not too big: 6 inches long, just over 4 inches wide, and 1.5 inches high. Supplied with battery clips with 22" cable and 24" long 12V socket. It has 4 USB outputs, 3 of which are 2.4 amp and 1 are 1 amp. I will update it after a few months of use. Update: 10/21/15 I've used it about 20 times. At least 10 of them were on the boat when I had to wind the tow tube up and down. That's such a good attitude. I have a cheap little bag to hold everything in. I've also used it to power my stereo when camping with the batteries from my diesel truck. Used it to start a small air compressor and turn on a light for fixing our 4 wheeler in the dark when camping and for a few other things. I am still very impressed with this small powerful device. Updated 7/9/17. Still works great. I keep it in a small purse. It's always in my truck now except for boating season. Then he gets used to the boat.