A Power Washer (PW) is are real useful tool these days. I use it to clean the underside of my lawn mower after I use it, to clean my concrete steps and porch, to clean my driveway whenever I want to seal it, to clean my vinyl siding and deck, and I'm sure there are more uses but they escape me at the moment.
Anyway, depending on what you're using it for is how you want to buy/rent it. I, personally, don't use over 1400 PSI on my electric Kartcher to clean the deck. (It may require more PSI to clean cedar but I can't speak to that.) The key to using a power washer is learning how, and how NOT, to use it. You either don't use it, or use it at low pressure, when you're operating it on things like windows, doors, and soft/explosive-like material. THe pressure from a PW can do some real damage! You don't want to use so much pressure that it splinters the wood. That's a no-no. (Just use enough pressure from a 'safe distance away' that the material gets clean. You can inadvertently use over-kill on a project!
I'm sure the Owner's Manual has more to say 'bout that. I DO suggest you read it, twice. There are gas and electric-powered models. The gas-powered ones are for off-site work and for working where an extension cord would be, well, prohibitive or too much work. I have one with a 'mixing attachment'. Other than that, shop around and have fun. THey're the best Super-Soaker around.