Adding to the concensus, I wouldn't use a cheap PSU on a mid to high end PC like yours.
Budget PSUs are just about exceptable on cheap hardware under £150 IMO. Just expect a reasonable chance of failer and possible hardware damage.
A simple guild. IMO a PSU should make up at least 1/9th of the hardware costs of your PC. (There will be some instances where this won't apply, like lots of high cost lower power items like SSDs)
So add the value of you hardware (no software), divide by 8. If the PSU you are looking as is lower then it's probably not good enough unless it's an amazing bargain.
Spending more is fine btw.
If this G7 is 20 A + 20 A on +12 V combined then it's really a 480 W PSU for use in a new PC. And pushing a cheap PSU to it's limit isn't recommended.