He has 16 amps on 12v rail....Will it work??
It will , but as I said it would be like walking on razor edge. Do keep in mind i arrived at that figure after assuming a non oced sandybridge pentium.I assume your friend would be having something older with a bigger power footprint.Add to that that most generic smps lie about delivered power and the factor of capacitor aging when used for a considerable period of time
If possible ask him to upgrade a decent psu, not only for his gfx card but overall safety and reliability of the system over the years.Its like a investment.
Incase he cannot owing to financial reasons, if his older psu is has been used considerably over 4 years, i suggest changing to a more decent and newer generic smps that one gets for 500to 1000 bucks(zeb 450 gold)
HD 7750 should work with all crappy PSU's out there considering its load power consumption is about 40's..
Nope its 55W, read here :*www.tomshardware.com/reviews/radeon-hd-7770-7750-benchmark,3135.html
It will work but i personally advise against using it a old generic smps/