Hi newcomer and welcome to the Tom's hardware forum.
Here are the system requirements for the 4870ATI Radeon™ HD 4870 Series System Requirements
ATI Radeon™ HD 4870 System Requirements
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)
Certified power supplies are recommended. Refer to http://ati.amd.com/certifiedPSU for a list of Certified products
Minimum 1GB of system memory
Installation software requires CD-ROM drive
DVD playback requires DVD drive
Blu-ray™ playback requires Blu-ray drive
For a complete ATI CrossFireX™ system, a second ATI Radeon™ HD 4870 graphics card, an ATI CrossFireX Ready motherboard and one ATI CrossFireX Bridge Interconnect cable per graphics card (included) are required
The recommended PSU is for the entire system.
U can go with this Antec 650W
are more that the PSU that u need, but can handle ur future upgrades.
Coolermaster don't makes a very good PSUs, so, try to avoid it.