I'm looking to upgrade the graphics card in my PC and I am just wondering whether my PSU is sufficient to power either an HD 7770 or a GTX 650.
My current PSU is an Aywun A1-3000 420W (the PC was built by a shop). Now I know that many of you will jump in and say that this PSU is a pile of crap and that it will explode etc etc, and I have read one person's story of this PSU failing on them, but they were using rather high end, power thirsty components (Core i7 CPU, GTX560, 8GB RAM, extra case fans etc).
My system is (minus graphics card):
AMD Athlon II X2 260 3.2GHz
ASRock N68-VS3 motherboard
4GB DDR3 RAM (single channel)
3x 500GB HDD's
LG DVDRW/CDRW combo drive
mATX case w/ one fan
As you can see it is very modest, and I have read that both of these graphics card are very conservative in their power consumption despite requiring a PCI power connector.
On topic, there isn't much data available for your PSU, but it is likely to work. Hd7770 is rated at 80W, GTX650 at 64W.
There is also the HD7750 at 55W, which doesn't require an additional PCIe connector, but you loose a bit of performance.
Without the data for your PSU (the sticker on it) it's kinda hard to be sure, but it's likely that any of those graphics cards will run. If you are planning on running the PC for a while though, a solid 400-500W PSU would be a sensible investment.
Generally, so long as you have enough pins for all your stuff, you should have enough watts. But I really would get a better PSU if you can. If those things break they can fry your motherboard or Hard Disk. It's just not worth the risk.
For a system using a single GeForce GTX 650 graphics card NVIDIA specifies a minimum of a 400 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 20 Amps or greater and that has at least one 6-pin PCI Express supplementary power connector.
For a system using a single Radeon HD 7770 GHz Edition graphics card AMD specifies a minimum of a 500 Watt or greater power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 23 Amps or greater and have at least one 6-pin PCI Express supplementary power connector.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.
You may find power supplies on the market that supply more than enough Wattage to run the system. However, some of them lack Sufficient Amperage capacity on the critical +12 Volt rail, which is necessary to properly power the critical components in the system (i.e. CPU and GPUs). This is the reason why graphics card manufacturers may overstate the power supply wattage, usually by at least 50 Watts, in an attempt to take into account some of those power supplies that have the weaker +12 Volt rail(s).
Your Aywun CLASSIC Power Series A1-3000 is rated at 420 Watts Peak Power not continuous power. The 3000 in the model number would tell me it's really a 300 Watt power supply. Aywun does not publish or show any +12V rail specifications so that tells me they're trying to hide something.