Honestly not trying to be a spelling cop but only because umlauts are fun to a nerd like me, it's Kärcher. Without the diacritical marks, it's Kaercher. But they've been moving away away from diacriticals in Germany, due largely to electronic typesetting and the Internet, which I think is a shame...and boring.
I also had a Kärcher pressure washer that crapped out after about a year, so I'm not sure that I'd take a chance on their shop vac unless I got some good feedback from other users.
Brett
Peters Creek, Alaska
Man is a tool-using animal. Nowhere do you find him without tools; without tools he is nothing, with tools he is all. — Thomas Carlyle (1795-1881)