Hi, I had the same problem when I left on holiday without my original charger; I bought a replacement on Ebay but that would not work. I also tried all the advertised alternatives, ie, used my wife's I-pad charger, no joy, tried a car ciggy connecter, no joy, tried a hi-power mains charger I use for a video camer;, no joy, tried connecting it thru a USB cable to my laptop, no joy.
When I got home 2 weeks later I connected my original charger and hey presto it started charging all the way up to full I phoned Samsung Technical to get further info( I previously worked in Korea and had contacts within Samsung Korea while there) and it was confirmed to me that just like the new I-pads, Tabs have a software prog that "recognises" genuine chargers(and by corollary) will not recognise third party chargers or methods(for I-pads the connectors are now called Lightning Connectors and only Belkin is authorised as a 3rd party supplier, to sell these, other than Apple...about £15 against £25 from Apple). For info, anyone with an I-pad can use a 3rd party connector once only, by switching the I-pad off and then on again when it will charge once only before X-ing out the charge.
Again, for info, after re-charging my Tab with the original charger and when discharged down to 70% charge, I again plugged in the 3rd party charger, the ciggy lead, and a USB cable, and none would re-charge, each showing a red X across the battery icon.
Samsung will replace a charger if it is less than 6 months old or will supply a replacement at cost) and remember the Tab itself is guaranteed for 2 years(I was not aware of this until I spoke to Samsung Tech), and unlike many other manufacturers, Samsung recommend that customers return under-guarantee products to them and NOT to the shop where it was bought(I have had a very poor experience with Carphone Warehouse in this regard where they said my I-5 was beyond repair yet I was talked through a software re-set by Samsung Tech.).
Again just for the record I am not a Samsung employee nor am I connected with them in any way.
Hope this may help some of the people who have posted in various places their problems with Tabs not charging, but from my own review, most of the problems have come from the use of non-Samsung chargers.