Fortron (FSP Group) Have long been a manufacturer of high quality PSU for over a decade. They were responsible for the first 120mm PSUs used by quality case brands such as Inwin and Aopen long before Corsair et al started selling rebranded PSUs manufacturered by the likes of FSP and Seasonic.
If your PSU is in good working order, it may well be strong enough for the 7850. I can't see that card needing more than 30A on the 12v rail. Which Fortron PSU are you using? You should check its output ratings on the sticker. Secondly, it is unlikely that a small bump to the GPU clock without also bumping the voltage would actually stress your PSU signficantly more, assuming your 7850 is stable at default clocks.
Theres always know-it-alls who blame the PSU. I feel sorry for all the people who have unnecessarily bought PSUs due to people who think they know more than they do about electronics. Suggesting that you need a 700-800w PSU for the system you detailed is proposterous - a good 450w would be fine, or a 550w if you want breathing space for adding power hungry components. And unless FSP have taking a steep dive over the past couple of years, don't worry about your PSUs manufacturer. Like I said, theres no shortage of people like zenzu888 who falsely put themselves forward as gurus.