HP Spectre/Envy laptops models ship with a USB-C Power Delivery charger, and in most cases any PD charger rated at or above the original brick’s wattage will charge it at the same speed — the device negotiates only what it needs.
For most HP Spectre/Envy laptops configurations, a charger in the 45W class (20V/2.25A) covers normal use, including light charging while working. Higher-performance configurations under heavy load may draw more power than the charger alone can supply, in which case the battery makes up the difference and slowly discharges even while plugged in.
A charger below the device’s minimum threshold will still charge it — just more slowly, and possibly not at all while the laptop is under heavy load, since the system prioritizes running hardware over topping off the battery.
Match or exceed the wattage on the original charger’s label. A quality third-party 45W GaN charger will charge a HP Spectre/Envy laptops just as fast as the bundled brick, usually in a smaller form factor.