It looks like a custom not quite ATX sized power supply.
Only the highest end cpus ever touch 150 watts. For instance most Core2 Duo chips had been rated at 65 watts. While a 2600K is rated at 95 watts a 1366 I7 920 was rated at 130. Both draw less then this unless pushes VERY hard.
A 7770 will not push past 50 watts. Long shot from the 100-300 estimate.
I do give you full(any users recommending a power supply[far safer, but may be hard with the OP's system]) credit. It will depend on what else is in the system.