[Kromm]

Be very careful sticking power modifiers on Energy Reserve. In general, you shouldn't. Almost all modifiers permitted on ER concern one of two things: (1) what the ER can be used for (e.g., just one power of a given source, just abilities, or just extra efforts and stunts), or (2) conditions on recharge (slowly, only under special circumstances, etc.).

Something like ER (Magical) or (Psionic) is already limited to powering magic or psionics, so you can't get a discount for it only working with magic or psionics. The reason why you pay 3 points/level for ER just as you do for FP is that while FP works with anything and thus is more broadly useful, ER can't be drained, has no bad effects on your health when low, and recharges no matter what you do. Those benefits are considered sufficient to balance the drawback of being limited to one power source.

There are older GURPS books that suggest things like Fatigue Points bought with limitations like "Magic only, -20%" or "Psionics only, -20%." That's fine . . . it amounts to buying an ER that can be drained, recharges only when FP would drain, and so on. It isn't a vey good deal, really, but it's legitimate.

However, those limitations ("Magic only," "Psionics only," etc.) aren't valid for Energy Reserve, which already has such a limitation built in. They're also not power modifiers.