|"What does that mean?"|
You have a 300W unit with a single +12v rail at 19A. It will work for the HD4670 but if you want something better, you'll most likely have to upgrade the PSU.
This article should help you find a card in your price range:
After reading the above article, let's say you decided on a GeForce 9800GT. Next thing to do would be go to newegg (or a similar site) & see what's available. Look at the specs for several of them, paying special attention to the requirements. For instance:
"Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 26 Amp Amps.)
An available 6 pin PCI-E power connector (hard drive power dongle to PCI-E 6 pin adapter included with card)"
Obviously your PSU wouldn't be up to the task.