Portable projector charging typically uses USB-C PD, often 45-65W. Portable battery-powered projectors need meaningfully more power than phones or tablets, so a standard 20w phone charger will charge one very slowly if at all.
What to know
Check the connector and rough wattage on the original charger before assuming a generic one will work well for a portable projector — small devices are forgiving, but power-hungry ones like projectors are not.