GURPS Dungeon Fantasy Treasures 1: Glittering Prizes

[Kromm]

From the description of Energy Reserve: "Each level of Energy Reserve (ER) gives 1 FP that you can only spend to cast spells of one type." It's an advantage that holds FP and applies special conditions to those FP; it doesn't establish a new, separate currency called "ER." When you spend energy points, they're FP whether you take them from your FP stat, your power item (which canonically "holds extra FP for casting spells"), or your ER. It's just that each source has different rules for how the FP it contains are spent, drained, and recharged. It's like comparing financial instruments: They might differ in how they're treated for the purpose of taxes, IRAs, offshore banking, etc. and have very different degrees of liquidity and portability, but they're all still measured in dollars, pounds, euros, or whatever, and can often be combined for specific purposes.